the problem is the inlet to fridge cold air hole has become distorted due to ice build up
remove the cover in freezer compartment and you will find opening which has become distorted due to ice build up, fix by building up with (knead it aqua) from local hardware store , this area must be level when putting back cover back into freezer.
may have to add piece of foam sticky back door seal to get good seal.
just fixed daughters had same problem.
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