Ok what you may find is the evaporator inside the freezer will be blocked so the cold air cannot be blown up into the fridge section. As all the cooling is done inside the freezer.
What you need to do is either a full defrost for 24 hours with the freezer door kept open and this will allow the ice to melt away.
Or take out the baskets inside the freezer section and take off the back panel. From there you will see the evaporator. Now you will need to use a hair dryer and melt all the ice away with it.
Once this is clear refit the panels and see how it goes from there.
If it does it again in say 3-4 weeks then you will have a fault on the defrost side. Either the defrost heater or the sensor in there will be faulty and will need to be replaced.
If you need anymore info just get back to me.