When my son was born me and his mother was not married, I filled out the paternity form at the hospital. A year later we broke up and she married another man and allowed him to legitimize my son by saying he was his biological father . She knew he was not. I looked for him for years and only last summer after her and her husband was separated did I get to see my son. Only to find out that he carries her husbands last name. Recently she lost custody of my son and their to girls to her ex husband. When my son came back around last year I had a perternity test done to prove that he is my son. What can I do to get my son back. They both lied because they both knew that he was not his son. My son was 3 before she ever met him.

There is some very illegal things going on here. First, a birth certificate cannot just be modified to add a father.

If you filled out a paternity form at the hospital, weren't you on the birth certificate?

Where were you while all this was going on? Were you paying support to the mother at any point?

I would highly suggest getting a lawyer who can dig into the legalities of what your ex did and assist you in getting back with your child.

Not sure that the OP says the truth

I have to agree with GV70 here. There are many points about your story that don't ring true.

As Steve points out if you completed an acknowledgement of paternity, then it would be hard for them to just change the birth certificate. When you broke up did you go to court to file for custody?

Have you tried now to get custody?

Another point of concern is your asking what to do in this case, yet you seem to think you can offer advice to other people in similar cases.