Two possibilities spring to mind. 1. Have you got or can borrow a fridge thermometer? It may be that the thermostat has packed up (can you hear the motor running all the time?). 2. Some fridge freezers only have one thermostat (in the freezer compartment), and if the freezer cabinet is clogged with ice, the motor may run continuously to try to reduce the freezer temp - this will over-cool the fridge section.
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