What is the correct procedure for changing from a Non-B visa to DTV in Hanoi, especially regarding cancellation of the Non-B and work permit?

I checked with my employer since my contract will end at the end of this year. The process is that you have to cancel your work permit first, and then cancel your visa at the immigration office. After that, they’ll give you a 7-day grace period to leave Thailand or prepare for a new work permit.

Note: your visa isn’t automatically cancelled just because you go abroad.

As the other poster above says. Cancel WP first. Get the B cancelled at immigration then they give you 7 or 14 days to leave the country

If I were you, I would not trust the school to properly cancel everything unless you've been working for them for many years and they've demonstrated that they've done everything by the books the entire time.

The problem with trusting them to cancel everything without you seeing that they did is that they might not. Or they simply "forgot" or any other excuses.

Then what's going to happen is that even when all your paperwork for the DTV is in order, they'll have no choice but to reject because your Non B is still active.

The last time I left Thailand 3 years ago, I went with the HR lady to cancel both my Non B and work permit in one go and got my passport stamped showing proof of Non B cancellation.