I believe you have 1 month to appeal. Do it. It costs nothing but the cost of a stamp.
Make sure you add as much documents/proofs you can find.
My situation is different, but appeals can work. I appealed one of their decision, they didn’t even show up to the appeal, they had an automatic 15 days extension and during this time, they decided I was right in the first place, so the appeal closed and they sided by me.
The whole thing took about 7 months I think.
They are extremely understaffed, I truly believe noone actually looked into my request in the first place.