@Mark *******
ups will eventually settle with thai customs. They will send you a bill, that they not so politely tell you that you have 30 days to pay before they add 10% as late fee. Idk if that's Apr or flat cost. Make sure, that if you've already made any payments to/through ups thailand, that you have screenshot or other receipts.
As far as letting the package go, if you haven't provided any identification numbers, I can't see how they would track you. Save looking up the return address