Two possible reason:
1) She is desperate, has no control and is trying to mess with you.
or
2) There really is a possibility that you are not the bio-dad
I think the first one is the likelier of the two. But, even if the second WERE true, your child knows YOU as the Dad. Recent court cases have found out that certain dads weren't the bio-dad but they were still required to pay the support because it is in "the best interests of the child". Your case could be a great example of the reverse situation. Regardless of who the bio-dad is, YOU are the real father. But, as I said, earlier...I think she's trying to get into your head, get you doubting that you are the bio-dad and mess with you...keep us informed.
1) She is desperate, has no control and is trying to mess with you.
or
2) There really is a possibility that you are not the bio-dad
I think the first one is the likelier of the two. But, even if the second WERE true, your child knows YOU as the Dad. Recent court cases have found out that certain dads weren't the bio-dad but they were still required to pay the support because it is in "the best interests of the child". Your case could be a great example of the reverse situation. Regardless of who the bio-dad is, YOU are the real father. But, as I said, earlier...I think she's trying to get into your head, get you doubting that you are the bio-dad and mess with you...keep us informed.