It sounds like he has no proof a child exists. I would ask for a copy of the birth certificate. Then I would check to see if the birth certificate was recorded with vital records/dept of health. Make sure the dates line up and that the one sent to you has not been doctored.

If everything lines up then you need to get a dna test. If in the U.S. she can sign up for child support and you may get one for free, or you can pay for one on your own. Do not sign or agree to anything without an attorney.