Brake calipers seizing

Drivers rear caliper was sticking. Horrible squeeking noise and excessive heat coming from wheel. Had new caliper fitted at a cost of £300. One week later passenger rear doing exactly the same. I can't understand why they are seizing. Subsequently I now need new pads and discs because they have been rubbing that much. Don't know if this is related (VW don't think so) but last year I was having issues with auto hold not releasing. VW said it needed a handbrake software update. That was done but the problem was worse than before. VW had it in for the day and they reckon the auto hold button had had a drink split on it and said they would replace it for £180. I said no thanks and I have had auto hold turned off ever since.