Hotpoint RLA64T Fridge new thermostat not working

Hotpoint RLA64T fridge went warm, compressor not running. Disconnected white and brown wires from thermostat, connected together, compressor running. After several hours fridge cooling down nicely. Concluded thermostat failed. Obtained new thermostat from Hotpoint/Indesit and installed. Compressor started and then ran continuously. Not tripping in/out on new thermostat. Possibly faulty thermostat, Hotpoint didn’t want to know as I had fitted it myself. Obtained another thermostat from UK whitegoods, another genuine Hotpoint/Indesit (111457 on bag)Danfoss unit same as the one from Hotpoint. Installed with same result, compressor running continuously. I binned the original failed thermostat but think it had three connections on it marked 3, 4 and 6 with the white and brown wires connected to 4 and 6. The new thermostats only have connections 3 and 4 available, there is no connector spade in the 6 position, so I have connected to 3 and 4. Have I been supplied with the correct thermostat? Is it possible that the replacement thermostats are wrongly calibrated eg for fridge freezer or freezer. Is there a relay or other interface between the thermostat and the compressor that could have failed? Is there a possible other problem? I am currently using a mains time switch to switch on and off, it gives coarse control which is ok for now will I try to find out what the problem is. Don’t want to scrap fridge as it seems to be a control problem which should be fixable. Would be grateful for any ideas.