Im afraid for this fault that you have its a fault on the fridge itself. If its freezeing when the dail was turned up and lost its cooling when you turned the dial down then its a thermostat fault.
Ive replaced many thermostats in these for this kind of fault that you have here.
To fix this fault you need to replace the theromstat at the top of the fridge behind the control panel. With this replaced you should find it will sort itself out with the cooling in there and be back to normal from there.