Make the sump deeper so the bottom is well below the frost line might help. My guess is that the frost line could be around 4-5 feet (say 1.3M) or more. You should be able to find that out. My thought is that as the ground freezes, any water that gets in there has nowhere to go. Maybe, if you can get to it, redo it so that there are some drain pipes going out from the bottom so that it has a chance to percolate into the ground. A much more expensive option would be to go through the trouble to make a connection to the town's storm sewer (if there is one on your street), but the permitting, and tearing up would be extensive which is why that would cost a bunch.