The freezer works fine; the refrigerator isn't cold.

The fridge gets its cold air from the freezer through a vent(damper) between the freezer and fridge.The fan in the freezer blows air through it. Make sure this fan is running. You may have to hold the door switch in for it to run. There is a flap you adjust with the fridge temp. control. Make sure it's opening and closing when you adjust the fridge temp.
The problem could be the electronic control if you have one or the mechanical linkages.

If the evaporator coils behind the back panel of the freezer are icing up because of auto defrost failure that will stop the circulation of cold air and eventually affect the freezer too.