Are you able to rotate the active ingredient in the worming tablets? Not sure if you're supposed to do it (or if they even make tablets with a different active ingredient) with dogs & cats, but with horses/cattle etc you're meant to change after every few times.

have you taken the cat to your vet? As Natasha said there may be an underlying issue, at the very least your vet should be able to tell you how to get rid of them.