I have answered this one many times, my advice will always be the same. Whilst some proprietary flea treatments will work on occasions, they are expensive and rarely work effectively, if it fails you have wasted that money and then you need to buy more of the same for it to fail again. After doing all that it has probably cost you more than a professional pest control treatment that is guaranteed.
I was a pest controller for 13 years and even we struggled to eradicate fleas sometimes with far superior chemicals than are available over the counter.
Don't waste your money, get it treated properly and make sure the treatment is guaranteed.