This is not unusual. They essentially see you as having said 'F*ck You!' to the school, so now they are essentially 'f*cking' you back!

If it's causing you a problem, you could write to the local FEB (Foreign Expert's Bureau) and explain your case.

Until that permit is either cancelled, or expires, you will struggle to get another one. Schools use this tactic on people who renegue on their contract, quit before their contract expires, run away, etc etc. Contracts in China are only really enforceable when SCHOOLS want to enforce them and they will often, if not ALWAYS, try and screw you in the small print somewhere.

Either way, you've made your message crystal clear. Don't renegue on a contract once a work permit has been issued.