He told me he was my dad but I did not believe him.
Why didn't you believe he was your dad?
I did not believe him because I've never met him before
Being skeptical about someone claiming to be your family that you never met is normal. Strangers shouldn't approach you and outright say they are your family, they should find alternative means to reach out and have a discussion on that subject. Outright saying that you are a family member the someone you just met will immediately be met with distrust.
I'm going to find out more and confront him about it.
I'm glad you are going to confront him and get to the bottom of this!