Neff Fridge at 12C

I have a Neff “non frost” fridge freezer. The model is K3990X6GB/06.

First noticed the ice maker not freezing ice. Then the milk started going off and using a fridge thermometer , discovered the fridge at 12C as opposed to the expected 4-5C. So did a manual de-frost for 12 hours, losing a lot of frozen stuff in the process. This seemed to fix the fridge [back to 5C], but the ice maker compartment was well over freezing still, so no ice.

Roll on 4 weeks, the fridge is back to 12C. Happy days. Done a bit of googling and I suspect a large ice monster has build up and stopping the air flow. I suspect the cause is a blocked drain hole, but that is now hidden behind the plastic compartment panel, and looks designed on purpose so only a “Neff engineer” can get it off.

Neff customer service have been terrible [they can legally only quote the manual, which is useless].

Looking at a £95 minimum spend to get a Neff engineer out to pull the back off and tell me probably what I know.

If this sounds like a rant, it probably is, but would appreciate any help if anybody has come across a similar case.