Why can’t I get rid of fleas??

Since I moved into my new apartment ( below dogs that are constantly walking by and sniffing my door ) I have had fleas every month

First, i didn’t know it was fleas and I only found one so I washed all my things on hot and vacuumed.

Then I found fleas on my cat ( maybe 4? ) and gave both my cats a treatment, washed EVERYTHING I OWNED and then flea bombed my ENTIRE house. I was so thorough and I vacuumed a few days after.

I just flea bombed my house AGAIN maybe 3-4 days ago but it has been a month since I gave flea medication ( I forgot to pick it up ) and I vacuum 3 times a week at least but I found another flea on my cat this morning…

I had a feeling the fleas were back so that’s why i’ve been vacuuming and using treatments but I didn’t find any fleas until today despite the cats being itchy.

I only find maybe a couple fleas everytime, I’m SO thorough. I can’t keep doing this, how the fuck do I get rid of them for good???

Is it coming from upstairs? the apartments are so shitty and they let their dogs sniff and come up to my door - additionally all the dogs are temporary because they dog sit for rover so it’s just a revolving door of dogs.

i’m so fed up, i’ve done everything. I’ve never had carpet before but is the carpet also an issue? please for the love of god how do i get them gone without over doing the chemicals on my cats and my home, I’m already treating both of them multiple times