Hi, I'm in Chiang Mai with a US passport. I extended my 30-day visa-free period at Promenada Mall immigration March 8, and it's good until April 9. I didn't know about this group yet, so I incorrectly went to Airport Immigration first. I have a letter from US embassy asking for C-19 extension ... should I go to Immigration near the airport, or is Promenada still the place to go?