There are several different issues here.
"So we are currently not sending any data to him?"
You label this as a question—it isn't. In English the question might be, "So are we currently not sending any data to him?" This has the verb and subject inverted. In native speech you would be more likely to hear, "So aren't we currently sending him any data?"
- You say that the one-word answer 'no' to such a question is ambiguous. You are right. It is an ambiguity that can trip native speakers under certain circumstances. Here are some examples:
A: Are you going to the meeting tonight?
B. No.
A. Aren't you going to the meeting tonight?
B. No.
In both of the above cases, native speakers understand that B will not attend the meeting. The difference is in A's expectation. In the first example, A has no expectation either way and has no obvious preference. In the second, A is expressing a concern or expectation that B is not planning to attend. B confirms the expectation.
What if B does plan to go to the meeting?
A: Are you going to the meeting tonight?
B. Yes.
Again A has no expectation. B gives an unambiguous affirmative answer.
A. Aren't you going to the meeting tonight?
B. Yes.
Here's where the problems start. A has an expectation and B's answer contradicts the expectation. The answer is Yes, but the intention about attending is negative. A native speaker would clarify and could equally say:
B. Yes, I am going.
or
B. No, I am going.
Whether Yes or No is used in the reply depends on a number of factors, not the least of which is A's tone of voice. Another is the preceding context.
Because the question contains a negative, it is important to resolve any ambiguity and so, in both cases, B adds the clarifier, "I am going" and that clause removes all doubt.
The important thing to notice is that the Yes or No are (a) addressing A's expectation and (b) expressing B's attitude to that expectation. The final phrase "I am going" is what supplies the answer to the question.
Answer
This is not a double negative. It is a single word addressing the questioners expectation followed by an independent statement of fact (the answer).