I doubt the
ANA or PNG would get involved either way. Throwing their weight around for overselling a coin would make a significant percentage of the membership very uncomfortable.
The biggest lesson here that hopefully other people can learn from is never buy coins over a huge value jump raw especially ms coins. Theres a reason why they arent already slabbed if theyre being sold on the higher side of the jump when the slab would make them 100 times easier to sell.
I do hope you can return it or get store credit for it, but considering the bill of goods they already sold you I'm not very optimistic.