@Lila *****
your company has to file monthly social fund and they also will be fined 20,000 baht if not notifying you have left within 15 days. The day after that you left starts the 500 baht fine from immigration. The best is to notify immigration a couple weeks before you will leave so your passport is stamped with a exit date.
Trying to cxl your wp and your extension the same day is a bit complicated. It’s not a matter of just showing up at immigration and say cxl my permit. You have to show
1) Letter to immigration from your company stating you resigned on whatever date
2) copy of the company affidavit
3) Withholding tax filing. If it was August 7th, you need July’s filing. If it was August 6, you need June’s filing.
4) passport or ID card of director signed.
5) passport copy of Yourself
6) copy of work permit
7) if you have cxl the wp. The copy of that.
For work permit
1) Company affidavit ...one copy signed by director
2) company stamp
3) director needs to sign the cancelation form
4) original work permit.
You cxl both the wp and permit on the same day. You either leave that day or get additional 7 days extension to leave the country.