Sorry you are in such a bind, rogicoco! I can't help but wonder why the SA would tell you about the gold w/GHW if she didn't know its availability. I can understand her wanting you to get your dream bag, but she should have made a point of finding out if it was available while you were in the store, rather than making you wait 2 days PLUS transferring the details to another SA. Obviously things were lost/mixed up in the transfer. I would insist on a refund because the bag you were charged for was NOT the bag you agreed to buy, but it does make things complicated that your SA is on vacation and can't vouch for your request of gold w/GHW.
I hope this all works out for you! At the very least, like everyone said, you may be able to exchange for another birkin in a different color. I would hope they would honor the price pre-increase due to the mix up.