Most of the mite treatments only kill the live mites, but not the eggs. That is why they keep coming back.

PAM (provent-a-mite) seems to be the best mite remedy there is. I don't remember for sure if it actually kills the eggs, or if it is just that it leaves a residue that kills them as soon as they hatch. Either way, it gets rid of the mites for good with one treatment. You will probably have to order it online.