Some of the hotels we have stayed at, have had small mains- powed fridges. I don't recall their makes. When we had a refrigeration engineer look at our freezer a few years ago, one of the things that he mentioned while we were talking, was that, in very hot weather, when a fridge couldn't get cold enough, one solution was to use a fan to blow air over the external heat exchanger so as to increase the rate of heat removal. This was in the context of the commercial fridges found in shops, but the same principle would apply to a domestic fridge. You could perhaps try using a small 12V fan if you have room behind your fridge.