@Izeb****
you need to start understanding HOW you are able to be here.
IF you FLEW here and entered at the airport and were stamped in free for 30 days you got in on a 30 day visa exempt entry by AIR..
THEN if you went to Vietnam and FLEW back you entered thailand AGAIN by AIR.. :O
(You said you got a 30 day extension at the immigration office but that doesn't count as any entry :/)
SO if that is your entry history THIS year (since Jan 1st 2020) you have NO 30 day visa exempt entries by land yet this year.
And as I said you can get TWO 30 day visa exempt entries by land in a calendar year..