UPS and FEDEX make it sound like you are a hardened criminal. They are working off the import paperwork, not what Thai customs is saying) tell them it is a mistake and tell them return. They may, or may not but it is a scam (sorta) for their import license.
It's been six years now but all I did was follow their instructions and mailed it to the US embassy with all the pre-paid return envelops. I think it took about three weeks.
Welp, I don't know anything about $100k and I have all my former state side address coming here, to include SS and have not had a problem. That may change tomorrow, however. A former neighbor who had been here 23 years said he used his stateside address for his SS with no problem. All I know is I file my taxes via Turbo Tax and also the FBAR to cover my 800k sitting in a Thai bank wasting away.
I'm in Udon Thani, been here for 13 years, three times I got the letters late for all three times they send them out except one time only got the middle letter and it was a month beyond the reply date. Had to send the form to Manila for them to input. I guess just the luck of the draw. It's the only mail I get except for updated credit cards.
Keep a US address for your social security. If not, you have to fill out a I'm still alive form yearly and hope that the postal system finds you here in Thailand.
We have the overpriced Fortuner. It's OK if you can keep the rats out of the engine compartment. My daughter has the Izuzu Mu-X which is cheaper and looks and rides great.