Have you heard of Orkin?
Orkin is probably one of the best and most friendly extermination companies you’ll ever find. They price their stuff fairly well too, so their service isn’t unreasonable. My recommendation is to immediately look them up, give them a call, and schedule and “appointment” for them to look over your house. They won’t do anything (e.g., start applying bug killer pesticide) without your express permission.
In the meantime, my other recommendations are to take out the trash frequently, spray your trash cans with Lysol, Oust, or similar, clean your house, and turn off the lights when you’re not using them.
Trash= fly attraction. Ever seen a landfill being filled before? Nasty- always has flies. I’m sure you already knew trash is a fly attraction, but emphasis is sometimes necessary as not many people come to think about it.
Clean your house= fly infestation. Probably the main reason you’re dealing with such a massive fly problem is that the fly problem is in your house. Literally- flies are most likely just reproducing in your carpet or furniture without your notice. This is not to creep you out, but to inform you of the situation. You can murder as many of the buggers as you wish, but for ever 1 you murder, 10 more will be born. Flies are mass-reproducing machines, similar to salmon.
Also, cleaning your house reduces the appeal to flies. No more are there those microscopic pieces of food and pet dander to feast on, or human dandruff. No more is there that comfy grit-filled carpet to nuzzle in and comfortably reproduce in.
I too have had to deal with fly issues; trust me, I know what you’re going through. Send me a message if you have any other troubles!