Sevin is not a very effective mitacide. The active ingredient in Sevin is Carbaryl. Many insects and lice have develoed a resistance to it. It has been around since the 50s. Casportpony gave you some excellent advice.
Use permethrin and your problems will be over. Remember, you gotta spray every nook and cranny. You give mites one tiny protected area and you'll have a full-blown infestation shortly thereafter, no matter what you use.
The permethrin a doctor prescribes for scabies (mites) is a 5% solution. This strength is even approved for use on infants. Just about every feed store around here carries it. It also comes in a dust form.
Edited because I had a minor detail wrong.
Edited by bigoledude - 5/18/16 at 6:57pm