If it is the case, it probably means that he environment in which your pet lives is infested with fleas. As a matter of fact, and different from the common belief, fleas do not permanently live on the animal. Fleas are more often on the floor, in carpets, pillows, etc... Fleas "jump" on the animal only when they need to be fed with blood.

Treatments you are using kill fleas that are present on the animal. But as there are a large amount of fleas in the environment, new ones replace the dead ones giving the impression the products are not effective. Therefore, THE ENVIRONMENT NEEDS ALSO TO BE TREATED.

One it is treated, you will have to prevent fleas to come back by treating them as soon as they re-appear with a shampoo, a powder or a spray. Ideally, you will have permanently on your pet a collar to be replaced as described on the packaging; it would protect permanently your pet against flease.