Cognitive bias
Recognising our cognitive biases can help us deal with fears of things that don't seem to exist.
A bias towards unjustified fear helped us in ancient times, so evolution selected for that.
When we were still living in the wild, if we heard rustling in the bushes, we could either think it's probably just a squirrel or something and not pay much attention to it, or we can think it could be a tiger and we go onto high alert, our heart starts racing, our perception sharpens, etc. If it's actually a squirrel, thinking it's a tiger isn't helpful, but we survive either way. If it's a tiger, and we thought it was a tiger, we're most likely to survive. But if we thought it was a squirrel, that probably wouldn't go well. So if there's some uncertainty, we're usually better off thinking it's a tiger and being afraid.
Even if it was unwarranted most of the time, a fear response still helped us on average.
But that isn't the world we're living in any more.
If you're walking down a dark alley (except don't do that), then a heightened fear response is still helpful. But it's not really helpful for day-to-day life in modern society.
Our conception of supernatural beings came about more recently, we haven't had as much time to evolve to deal with that, and there isn't that much survival advantage for one response above another to the supernatural. So we just take the same response we learnt with tigers and we use it for the supernatural. Except that you can't go and check whether the supernatural is actually hiding behind a bush in order to validate or alleviate your fear, and you can't just wait a bit to see if anything happens. So we're using the same fear response, but we can't use any of the ways we learnt to get rid of that fear.
Except that we still have 1 rather hefty tool in our toolbox: reason. Now, it's often not immediately that effective at dealing with emotion, but it can help over the long term to analyse emotions and why we feel them.
Arguments against the supernatural
There is one main argument against supernatural claims: lack of evidence / the burden of proof / the default position / parsimony / Occam's razor.
We shouldn't believe things that don't explain any evidence. Of course one can assert that a particular piece of evidence is explained by something, but simply asserting that doesn't explain why or how it explains it (i.e. where does this fate gremlin exist, how are the interacting with reality, why are they messing with you, what justification do you have for believing any of this, etc.). One could say a claim doesn't explain the evidence if it can trivially be swapped out for similar competing claims that explain the evidence equally well. We also shouldn't accept claims that explain evidence can be explained more simply, or that can be explained by things that also explains other evidence (e.g. "fate gremlin explains A and natural causation explains B" is less preferable than "natural causation explains A and B").
The reasoning behind all of this, roughly speaking, is that, if we are consistent in accepting unnecessarily complex or non-explanatory claims, we may accept infinitely many other things, which may include contradictory things, or we may accept infinitely complex things (consider the idea of living in a simulation - if we have no bias against that based on simplicity, we also don't have a reason to reject the claim that we live in a simulation which is itself in a simulation, or the claim that we live in a simulation which is in a simulation, which is in a simulation, etc. - that's not a good epistemology).
Let's say your fate gremlin would punish you for A, B and C through punishments X, Y and Z. We could imagine another being might punish you for D, E and F through punishments U, V and W. And another one for G, H and I through R, S and T. Etc. Some of these might be really bad, while others might be a bit more petty and punish you when you wear the colour blue by occasionally making a tomato you're eating sour or making you stub your toe.
And then you might imagine the inverse of all of that where there's a fate anti-gremlin that instead rewards you for doing A, B and C. And similarly for all the others.
Do you have any better reason to accept the existence of the one you believe versus all the others? You probably don't.
Lack of evidence is the main argument mostly because such beliefs are typically unfalsifiable (you can't prove that such a being doesn't exist), although there may also be other arguments against certain beliefs. If there were some powerful supernatural being after you, they'd probably be able to do a lot worse than whatever may have befallen you in your life (which is not to take anything away from how bad your life experiences may have been, but every moment of joy you experience serves as evidence against the existence of such a being).
Also, if there is such a powerful being, they'd be really petty and immature to be mean to one particular human among billions on this big rock, orbiting one of hundreds of billions of stars in our gigantic galaxy, which is one of hundreds of billions of galaxies in our colossal universe. It would be more petty than a child torturing ants for fun.
Another way to deal with fear is by making the thing you fear seem really silly, as shown above. Every time some minor annoyance happens to you, you could be like "Curse you fate gremlin!". That's just an idea, anyway.
Therapy?
You mention that you've spoken to therapists ("doctors"?), and I'd definitely recommend that you continue to do so, since they can help you make sense of and deal with what you're feeling and thinking.
Not all therapists are equally good, and it wouldn't be particularly unusual to need to try a few different ones to find one that works for you. I recently saw a video by Louis Rossmann making an interesting (if somewhat blunt) comparison of how easily we're willing to spend time and money on other things, and we may try various solutions to deal with a problem, but when it comes to our mental health, we're very quick to altogether give up on therapy if it doesn't immediately help (if we even try it at all). This may or may not apply to you, and it may not apply so much to someone who's struggling with money, but it seems worth mentioning and keeping in mind.
You mention that you're not religious, but you may still find some helpful resources from recovering from religion, since fearing the supernatural is a common problem for former (and current) theists. There is also the secular therapy project (mostly US-specific) that may help if you have a hard time finding therapists that don't try to solve your problem with one supernatural being by giving you a different supernatural being.