Trading Post item I bought is missing

You misunderstand.

The item I authorized purchase for (a very large sword) is no longer available to transmog at all.

Nobody in game is purchasing items for their underlying database value. They’re purchasing them for how they look.

The item I purchased is no longer in my inventory. I don’t really care what the database value happens to be.

Semantics is asking me to care about the item ID.

I’m asking for a refund. If they want to solve the cosmetic issue on their own time they’re free to do so, but with a refund I wouldn’t really care.