Hello, i have a question regarding non B cancellation letter

i resigned from my company and requested them to cancel the work permit and extension of stay by june 4th, which is also the last day of validity. They didnt cancel it on time and now they can only give me the cancellation letter one day late, on the 5th. I already have the documents for getting a non Ed visa, but i dont know if i can go apply without the cancellation letter, or even how said letter looks like. im afraid the comoany doesnt even know what im talking about, so i would like some advice on this,

a)do i need the extension if stay cancellation letter if my the extension ends on the 4th, same day as i plan to leave?

b)how i can communicate to the company what i need, in case they dont know?

thanks