What temp setting do you have the fridge set to, a defrost is the answer in terms of getting the fridge to operate again as the issue will be due to ice blocking the duct which takes the cold air in the freezer and delivers it into the fridge, however, this should only need to be done once in a blue moon not every week\few days.
If the duct keeps freezing this suggests the fridge is set to freezing, or something is causing excessive moisture which is freezing in the condensation duct.
Let me know what the thermostat is set to and double check the fast freeze button hasnt been switched on by mistake.
It sounds likely the thermostat has failed, a 24 hour defrost would normally be sufficient, and if it was cooling for a few days then stopped suggests there is a reoccurring fault.
The next step would be to test the thermostat, which is a case of stripping down the light compartment and using a multi meter to check continuity.
Should you not have a multi meter or prefer an engineer to attend, please provide your postcode so I can recommend a local engineer.