Work visa expired

Hi guys,
I've been working in China and resigned about a week ago. The company I was working for said my Z type would expire on the 30th of April. Problem is they still have my passport and I haven't been able to leave the country. They told me that it was the Chinese consulate and due it being labour weekend they were not open. I am worried that the only availability for a flight back to South Africa is on the 7th. Will the migration not hold me up for having an expired entry permit? What can I do?
Asanda