Picked up a Ball Python

[Kajitsu90]

I have a Ball Python named Caesar. I picked him up from the pet store a little over a week ago. As soon as I picked him up in the pet store I noticed he was covered in black mites. The worker told me they were having a mite problem and that it was simple fix. The next day I noticed Caesar was bathing for long periods of time and looked it up and saw it can be attributed to the mites. I picked up some reptile spray and washed him down and he seemed fine for a few days. Today I noticed they were all back. I soaked him and cleaned his home but I’m worried this isn't going to solve the problem. I get the ones off his body but they seem to be hiding in his face. :( Also he has white powdery looking substance around his eyes that have been there since I picked him up as well. Any help would be greatly appreciated.
Thanks