Your "Frost free" fridge is not cold enough into the refrigerator part ?
However, the freezer works very well ...
Your fridge thermofuses are probably blown !
Blown thermofuses stops the defrosting system. Frost accumulates in the freezer part. Cold air flow can no longer reach the refrigerator part. It gets less and less fresh ...
You can test the thermofuses using a multi-meter. They must be conducting. Otherwise, there are blown. You can therefore buy a new thermoses box kit including a defrost resistor for 60/100 bucks.
Or... you can 3D print this fuse case, insert two brand new fuses (~1 buck each on ebay) and then fix up your fridge !