Order the Provent-A-Mite and use exactly as directed (it does NOT get sprayed directly on the snake). It sounds like all the treatments in the past may well have killed the visible adult mites but didn't get the eggs which are just constantly hatching out more mites to breed and make more eggs. P.A.M. will break that cycle.

For now I'd strip that enclosure down to a bare minimum of stuff, clean it thoroughly, and just put down layers of pure white Viva brand paper towels instead of any loose substrate until this issue is fully dealt with. Also the water dish doesn't need to be big enough for your snake to soak in. It's likely soaking due to the mite infestation, as most healthy ball pythons do not soak on a regular basis.

If you got this snake from a typical chainstore type pet store it likely came with the mites. Anyways, it really doesn't matter where they came from, they need to be dealt with once and for all as mites do affect your snake's health.