Old fridge to cold after repair

Hello Forum

My old Hotpoint fridge 8221 has a burnt Starting Relay and packed up.
I looked online and appears ePTC 103N0050 is recommend for this model.

I fittted the 103N0050 yesterday, the fridge started up immediately.

However the fridge is to cold and freezing food and does not appear stop running the compressor ever.

Compressor does not appear to stop even with the
air circulation flaps closed,
thermostat on 1 and even tried pressing defrost button on the thermostat and turning to 0.

Other possible consideration the Fridge is in unheated property near London.
Door seals

I was thinking I next need to check the thermosat/replace if want try fixing?
So a universal thermostat?

Thank you
Iain