The persin in my sin because my not be his father and my son is 15. If it is proven by dna that he is not his father what happens with cs alrwady receive. And the guy on the because was informed of this before the child was born

Um... can you try this again in full words... I can't understand what you are saying.

Let me see, A man signed the birth certificate 15 years ago, knowing he may not be the father.
You are now divorced and getting child support.

Someone wants a DNA test ? Who ?

But this will depend on where you are at.
In some states ( if even in the US) you can not challenge the legal father, and the person on the birth cerficate is the legal father ( even if not bio father)

In other states someone ( bio father) can challenge, but only within a number of years.

In some states a challenge can be made, it would stop current support payments
Nothing happens about payments already made, those were made since he was the legal father at the time.

If a court awarded child support, it was because that person acknowledged paternity. That person is then the legal father. If it is later determined, by scientific testing, that he is not the father, he may be able to get support stopped. However that is subject to local laws so a local attorney should be consulted.