Frontline Plus Coupons

I've purchased Frontline from my vet in the past & it worked perfectly. My cats were flea-free for the entire month. I decided to save a little $ by purchasing it on Amazon. It didn't help at all. I may as well have just donated the $ to charity instead of wasted paper & packaging on this purchase. I'm not sure if the product was expired since there was not date on the packaging. I'll continue to purchase Frontline through my vet.