Can I extend my visa in Thailand or do I need to leave the country?

I dont / wont work here so this is second hand information but I understood also that when the employer cancels the work permit you have 7 days to leave the kingdom and its not possible (well not easy) to transfer to any other extension of stay.. Its a 'you must leave' 7 days. EDIT :: You can of course return for a new permission of stay.

Verify that but this is how I understood it.

You cannot extend a work visa without a bunch of employment paperwork. You need to leave and return.

Sadly (for you) there is no 30 day extension available at all on Non-B visa/extension

So that option is off the table 😕

You need to CANCEL your current extension of stay based on employment at the immigration office where you got it, then you could exit/re-enter the country to get a NEW free visa exempt entry stamp for 30 days..

You can use any land border you want (DO NOT USE the Aranyaprathet/Poipet border with Cambodia as you won't get back in)

BTW: Thailand doesn't have a border with Vietnam 😕 so if you are bouncing out and back by land you use Malaysia, Burma, Cambodia or Lao ..

This isn't a "where can I bounce the easiest group" sorry. Post on a group related to where you live and ask where people are bouncing out and back in that area for new entry stamps.