I actually am wearing a pair of the stingrays right now! All I can think is that maybe they could be the wrong size? Just speculation, of course. I bought my stingrays in my TTS and I literally have had 0 issues with them. I have worn them all day (and will be today) multiple times and no blisters/no digging. I would try the bandaid method (using a bigger bandaid that might not shift as much) or a heel liner, like others have suggested.