Beko AsGn542b cooling issues

Hi I’m hoping I can get a little help on our frost free Beko AsGn542b american style fridge freezer. The issues are a few things. Firstly the top 3 shelves in the freezer do not get cold enough to freeze food yet the shelves beneath freeze fine. The 2nd issue I believe it’s not defrosting as the coils are constantly frozen on the top but not on the bottom. I have checked the heater element using ohms law its reading right in the numbers 422ohms. (Unplugged) also checked the freezer defrost sensor which seems to be working fine too. There is a thing called a thermal insurance sensor fuse/ which I believe replaces the old thermal fuses that they used to use . Using the old way to check a thermal fuse if they have continuity they are fine however these new style fuses/sensors seem to only open when they hit a certain temperature usually in iced water. If anyone can shed light or give advice on this model or the components I’d be very grateful