This sounds a tad strange. Are you able to take a picture of this, so I can get a better understanding of the issue? Were the white dots there from the beginning, or were they caused by the case?
....sand corns get stuck between case and phone
....you take the case off 3 times a week
....3 times a week the sand corns scrape away the paint from the frame
It is clearly your own fault 🤦♂️
Clean it only if it really needs to be cleaned.
None of my phones ever hade issue like this so it may be poor quality of the color
everybody should from time to time to get of the case and clean out , not my fault at all