Have you checked whether the door to the fridge has dropped which means that the catch is not properly engaging , so that the light is not being turned off when the fridge door is closed. This happened on our Hotpoint fridge/freezer and after a while the heat from the light which was permanently on caused the temperature to rise. After we'd called out the engineer and he had adjusted the door hanging, it was fine. Try taking the bulb out of the fridge light to see whether this could be the result of the problem.