@Louis ******
so what you should do is take that letter as soon as you get it and go to the labor office early in the morning. Cancel your work permit effective the date on the letter for the future. Then go to immigration right after that and cancel your extension effective august 31st as well.
They usually let you do cancellations up to 2 weeks early and you're within that time frame now.
That will let you know if your work permit was already cancelled or not.
And you'll have to do both of these anyways so might as well get it out of the way for peace of mind.