Provent-A-Mite (PAM): http://pro-products.com/provent-a-mite/

Get it, use as directed on the enclosure, hides, and paper towels you'll be using as substrate. I repeated the PAM treatments every 7-10 days when I fought my last infestation. Unlike the product you are currently using, PAM persists for 30 days. Female mites leave the snake to lay their eggs in the enclosure - the PAM will get them as well as any newly-hatched mites during the off-snake parts of their lifespan.