You have my sympathies. I'm dealing with a seemingly unending stream of mice. My cat kills every one that comes in and I suppose I should be grateful that they don't get the chance to do any real damage, but I find the whole thing heartbreaking. I hate finding their tiny corpses.
If you could afford it, I really recommend getting a pest control professional to come and check your house. They won’t destroy anything if you don’t want them too, but they will help you find the hole. Check all around every pipe and your baseboards and anywhere wires come in.