Bests & Worsts Reviews from Amazon

I have used this product religiously every month purchased from a Pet store and my cats never had fleas. Since I bought 3 mos worth (for 2 cats) from here I had seen them scratching and this morning I saw a live flea in my house...which means there are many more. I am disgusted with myself that I did not continue to buy from pet retailer as I never had this problem before. I believe this product was counterfeit.