Can I Obtain an Emergency Extension in Thailand with an Embassy Letter After Visa Exemption?

Hello!

I arrived to Thailand on 11 March on visa exemption and i did one extension already until 9 of May. My flight to go back my country in the begin of May was canceled again. My question is if still i can do a emergency extension 30 days with the embassy's letter that allow me to stay until 8 of June.

If still i can do, where i should to go Chanwattana or Muang Thon Tani?

I have already the embassy's letter issued before the "amnesty"

Thank you for your advise.