If you are using Frontline Plus, keep using it regularly and be patient. Your house has flea eggs that are constantly hatching. Eventually they will be cleaned out it no new fleas are introduced. You are halfway there so don't stop using it. Don't buy generic! They don't work. Yes they have the same ingredients but are from China not Germany where FL+ fipronil is made(BASF). There is a water based house spray called Siphotrol Plus that can be sprayed in the areas the cat hangs out, couch, cushions bedding etc. It is very safe and will not hurt furnishings. You just spray from waist level as you back out of a room. Let it dry for an hour, no fogging. Frontline brand is worth the extra money. Costco sells it for what the vet pays for it. Advantage works well also but it must have an insect growth regulator in it. Seresto collars work but take a long time. Forget the borax stuff. Again, you are halfway there.