I have an american style Admiral 60ADi fridge freezer only 4 years old has stopped working. I had it regassed but it stopped working afte only 3 weeks. My dilemna is whether to buy Maytag (who own Admiral) warranty policy for a further £330 which will pay for parts and labour plus a years warranty or to give up and buy something else. The service at Maytag in England is appalling so part of me feels like not giving them another penny but the other part thinks it will be cheaper than a new one. The local engineer seems to think it may be an oil blockage.

Did the local service man find the leak? If it needed refrigerant it must have had a leak.
If no leak, you wouldn't have needed refrigerant. If refrigerant was put in and not needed that would make it stop working. I don't see how it could be oil blockage. That only happens when unit is laid on its back or side when transporting. Oil can flow out of compressor and into coils, where it gets in a low spot and can't flow back to compressor.

I think you need new service man.