Hi! I have similar problem. Stayed in China as student and travelled a lot on business (F) or tourist (L) visa later. Unfortunately, you can get PCC for time spent there as resident (student, work) only. But not for F and L visas. I obtained PCC for my study period, used an agent to do so. Costs money, but I'm not in China now, so it was the only solution. Some guys on this forum mentioned having same problem. Some got PCC for study and work time, the rest they covered by LoE. One guy claimed to get his PR already
I advise you to at least try getting a PCC, even if you cannot do it for the whole period, and then provide evidence showing you tried communicating with local police ect (like emails) or agents.