How can i fix my Hygena fridge/freezer, model 6826?

My Hygena fridge/ freezer, about 10years old, isn't working properly. Its operated by a single compressor and thermostat covering both units. The freezer appears to be functioning ok but the fridge only gets, down to about 8C irrespective of the thermostat setting. Additionally the compressor is working all the time and doesn't cut in and out as normal. It seems odd that the freezer is ok but the fridge isn't given that they're covered by one thermostat and compressor. Can you advise me on the most likely cause and the remedy please.