My hotpoint fridge/freezer?

I have a hotpoint future fridge/freezer. The fridge is playing up the temperature of the fridge is not cooling however the freezer is working fine. We have tried on a number of occasions to defrost the fridge for 48 hrs it works for a bout two weeks and then starts playing up again. Any ideas?We had a engineer come to try and fix it he defrosted it using a a hairdryer worked for few weeks and then went back to not cooling properly. Please help!!!