Try to treat your kitty and your house at the same me. To treat your cat: don't use the flea collar or Harz, use Revolution. But Revolution is month-based, so you don't expect to see the effect too soon. It takes time! Maybe a month, or two months. After you apply Revolution on your baby, it kills fleas and eggs in 24 or 36 hours, but you need to treat your whole room at the same time because the flea will still jump onto and bite your cat. Use Vet Kem products to treat your rugs, sofa, curtain, etc. You can only buy Vet Kem spray from your vet. YOu can also go to online to fine the nearest vet who carry Vet Kem produsts. Meanwhile, keep your cat indoor totally.
Another reason of what is hard to get rid of flea is the weather. When the weather cools down, your situation will be improved.
I had the same terrible experience last month. I just moved to Texas, everyone knows the insects of texas are very aggressive, and my cat got flea from outside. I had to work on it for three weeks as a full-time job!! Luckily, it's under the control now.
Hope it helps a little bit. Good luck!