It’s a real shame when an otherwise excellent product like the MacBook, and a well regarded service like AppleCare (reliability & service from Apple generally scores very well in surveys) falls short of the mark. Have you tried writing to an individual at all? If you have a local Apple Store it might be worth finding out who the manager there is and getting hm/her on your case. Also, publicity (or rather adverse publicity) can help things along - if things aren’t being resolved, then see who you can let know. I always try and get the person I’m speaking to to empathize and pose questions that they can’t just answer yes/no to, like “how are we going to resolve this” or “if you were me, what would you expect to happen in order to remain a satisfied Apple customer”?

I guess you may have already tried all this, but good luck anyway - hope it’s all worked out.