well, apparently there is some doubt otherwise he wouldn't be asking for a DNA test. It's not like it's something you can fake the results on, and if you're not his, then he shouldn't have to pay your mom anything. If he was 100% certain you are his, I can't imagine he'd ask for DNA testing. Not trying to be a dick, but that's the truth.
Regardless, that's a shitty position to be in as a kid and I'm sorry you've got to deal with that. And if you're trolling, I hope all of the bad things in life happen to you because that's a fucked up thing to joke about.