Neff fridge/freezer (K8614X3GB) behaving erratically

Hi, I have a problem with a Neff fridge/freezer (K8614X3GB) behaving erratically.

About a year ago I was finding the internal light was staying on when the door was closed, so sounded like a faulty switch. Ended up removing the switch and still the light stayed on? Ended up removing the bulb and left it as it was. Scroll forward 12months and last week the fridge just stopped cooling so both compartments thawed.

Ive now removed the fridge as its a built in unit. There is power but the compressor is not running. I loosened the control until (s/n#481318) on the inside of the main compartment to check it and on moving it the compressor started up! It then seemed to work fine for several hrs, getting the temps to -5deg/main compartment and -15deg/freezer, then it switched off. I decided to replace the controller unit, as I’d had the internal light issue before. Ive now done this and the fridge is still operating erratically and when moving the controller unit and harness, it seems to be just coincidence that the fridge it starts again. Also I re-installed the internal light and switch which works fine when the fridge is at room temp. As soon as the main compartment cools, the light just stays on as before, as if the light control is not just by the switch and is being controlled by smthg else that is affected by the cold.

Could someone advise where the thermostat is as I presume there must be one for each compartment? The fauklt does sound like a contol/sensor issue as when teh compressor runs both compartments seem to get to the correct temps.

Any advise would be most appreciated.

Thanks