When this happened to me, I did as Thai-Kiwi suggests and scanned colour copies of all the documents (for my own back up), but then, with some trepidation, sent the originals to TG's London office as I personally felt that was less risky than mailing them all the way to BKK. (I was very clearly informed that sending scanned copies would not be acceptable but I guess that may depend on which office and who you're dealing with as to how strictly they adhere to this rule.)

In the address, I made sure I included the name of the specific person I had been dealing with and sent the package registered post (so it would have to be signed for upon receipt and there was no way they could deny that it had arrived). This was in the UK but I imagine the US postal service would offer a similar option?

Fortunately this worked and I'm not sure what I would have done if it didn't but I guess I would at least have had proof of posting and back-up copies of what I had sent if it had become necessary to argue the case further...

Good luck. I agree it's a daft system...