Freezer misbehaving – temperature too low

Appreciate any advice on this one..

Fridge-freezer: Zanussi ZI9454X
Age: 9 years
Fridge working normally – stable temperature at 5 degrees C..

Freezer started misbehaving last week. Temperature rose to around -2, despite being set at -16. Digital display still working. Defrosted freezer for a full 24 hours. There was no excess ice or anything inside the compartment. No change when switched back on.
Called engineer. He replaced the “motor” saying the previous one had “burned out”. £180+£50.
Powered back up freezer. 24 hours later, the digital display says it is at 3 degrees, with a flashing red alert light. But the freezer feels very cold inside, and in fact a thermometer shows it be at -26 at the moment!

Phoned back engineer. Refused to return saying it was all fine. I should switch it off and on again, and put some food in the freezer. And that’s it.

So clearly something wrong with it – the freezer is too cold according to a thermometer, and the digital display is inaccurate. Not sure what to do now. Call a different engineer and write-off the £230 we gave the first guy? Or order a new PCB online and fit it, with fingers crossed?

Thanks for any help.