Release letter and FEC cancellation notice

Hi. I worked for the same school in China in 2 spells (2004-2009; 2013-2015). However, I left in October 2015 (after giving notice because of a family situation) and returned to my home country.
Shortly afterwards, the school contacted me and said if I didn't return to complete the correct paperwork (I wasn't aware at the time I left and they didn't mention it even though they knew I was leaving), then I risked not being able to return to work in PRC in the future.
I 'thought' I had a good relationship with them but when I tried to contact them again they didn't respond - I think they were unhappy I'd left even though they accepted it at the time.
I'm considering a return to PRC but wonder how I stand in regards to the documentation I should have got from my old school, (I now know this as being the release letter and FEC cancellation notice).
My work Z type expired earlier this month (unless the school already cancelled it).
Does it make a difference that I've left PRC so will be making a totally new visa application from my home country? Would it matter if I was applying to a school in a different province to my former school?
Sorry if my post is a little long-winded - Any info would be much appreciated.
James from the UK