Good afternoon, this sounds like a failed thermostat.
My suggestion would be first check the deep-freeze \ super cool isnt switched on, as this would override the temp setting.
With regard to the door seal a poor seal would be reason for a build up of moisture in the fridge (leading to ice on the back), and potentially the fridge not getting as cold as it should, since your issue is it getting to cold this would suggest a problem with the thermostat
The door seal is easy enough to change, but I wouldnt be included to do it until the thermostat is fixed, a replacement thermostat is around £40, plus £30 labour, the door seal would be around £20 and could be done by yourself.
If you would like me to recommend someone to come out and repair the thermostat please provide me with your post code, should you need anything clarified please do get in touch.
I would recommend you use an approved Smeg service engineer, your nearest service firm is Excel Services and they are 15 miles from you. The engineer can be contacted directly on*********** the second nearest is IRM Services and they can be contacted on 07976956157.
Should you find the authorised repair centres to extensive you could try a local firm called DJ Domestic Appliance Service & Repairs and they can be contacted on 07907 847467 or 07938 818935.
Should you need anything clarified please let me know.
Hello I am just following up from last week, do you still require assistance, if the above suggestion has resolved your issue I would appreciate if you could rate the service received.
Good morning sorry for the delay in responding, do you still require assistance?