What steps should I take if my employer won't return my work permit after resignation in Thailand?

I resigned from my job last Monday (June 24) and have yet to hear anything from my employer. This is very typical of them as they do not like “confrontation” or dealing with anything like this so they just go silent. They have had my work permit for months and I have been asking for it back, only for them to keep brushing me off and ignoring me about it saying they will give it to me.

I am currently on an extension that expires May 2020. From what I read on previous posts, I must cancel my work permit with the dept. of labor and my extension of stay with the immigration office.

My issue is that I do not have my work permit in hand, as my former employer will not respond to my messages or give it back. Another issue is that they will not write me a letter stating when my employment ended because they will not respond to any of my messages and are completely unprofessional.

Any advice would be much appreciated.