did you get the drontal pill the first time you found the worms? if you used the liquid medicine called strongid plus, that only kills roundworms (the little spaghetti or macaroni looking ones). if you have tape worms (the come out like little pieces of rice), you need to use drontal. drontal is a broad spectrum de-wormer that comes in pill form and works wonders! drontal is the ONLY thing i use for my cattery and i have even found it to be safe for pregnant and lactating queens. just make sure that you repeat the dose in 3 weeks so you don't end up with a re-infestation. the drontal kills the adults, but not the eggs so you have to kiil the eggs when they hatch so that they don't end up laying new eggs that will hatch into more worms.
PS-Ask your vet for a pill giver so that it's easier to give the kitty the pill. I never use anything but a pill giver because it is sooooooooo easy and my kitties respond really well to it!