How do I fix my leaky bathtub faucet?

I have a two handled faucet. One for hot and one for cold. It has been leaking for days but my dad is too lazy to fix it. I have searched and searched for a solution online but the only solutions are for different types of faucets. Ours is a washerless faucet that uses these plastic cartridges with O-rings. We took the old plastic cartridge out and replaced it with a new one...and the leak has gotten worse..we assembled it the same way we took it out. Does anyone know how to fix this problem?