I have been on a student visa for 18 months.

Recently I accepted a job offer and after a trip to Singapore, returned with a 3 month non-immigration visa, and a few weeks after this received my work permit.

Unfortunately the job didn't work out and I had no choice but to leave immediately.

I am not in communication with my ex-employer, but left my work permit with them, so maybe that has been cancelled.

My initial 3 month visa expires mid December (It was never extended).

It is my intention to start studying again in December and return to my school who will do all the necessary paperwork, but my concern is that I don't know what has been cancelled, what i need to cancel, if my current visa has now expired early, and whether I will have problems leaving the country to get the new visa, etc.

Any advice on these would be greatly appreciated. I will go to my school on Monday but not confident that they will know the situation.

Your 90 day entry you got from the visa is still valid. Only extensions end when your job ends.

It might even be possible to extend your current permit to stay based upon going to school if you can get the paperwork to do it.

Thanks for the quick reply and it's good to know the visa is OK for a few more weeks.

Will not cancelling the work permit be a problem? As I have no way of knowing it's status.

Also, I was under the impression that I would have to leave the country and return on an Ed visa to be eligible for Ed visa extension. Is it possible to get these education extensions on a nonimmigrant B visa?

The work permit cancellation has nothing to with your visa entry.

All that is required for any extension is a non immigrant visa entry the rules do not specify any class of visa to get one. There are some immigration offices that will impose their own rules.