Had a similar problem recently. My freezer worked well but the fridge was not cooling.
I solved the issue by switching off the unit .
Next open the front freezer compartment.
Use a hair dryer to defrost all the ice around the fan unit 10 to 15 mins on n off. I stuck my finger in the gaps to realise Ice was forming inside .
Install the top freezer compartment back and let the fridge cool off futher for 4 hrs or so. The longer the better.
The fridge should start to cool in 1 hour or so soon.
Ice building up in the freezer compartment had caused the fridge to stop cooling.
Another long n easy way out is to switch off the unit to defrost for a day or so. The drain hole could also be ice blocked.
It might work again hopefully after defrosting.. Hope this was helpful.