I had this problem with my corn snakes a few months ago. I have a herpvet that comes to our local expos and he recommended "Proventamite". That stuff works like a charm. Just make sure all that is in the cage are decorations and bedding. No hide or water bowl. He recommended either boiling those or scrubbing them like hell. Whichever is easier for you. The reason proventamite is actually pretty good is that it kills the larval, and egg stages of mites rather than just killing the adults. I highly recommend it.