son has to get degree certificate legalized in order to renew Residents Permit

My son is currently teaching in China. His Residents permit runs out in May and his Z-permit in July. The local immigration authorities have told him he has to get his University Degree Certificate legalized/notarized before they will allow him to renew his residents permit or give him an extension to stay until the end of school term. I have looked on the Chinese Embassy website, and think I know which documents to provide. Can I send them in the post to the consulate, or do I have to go in person? If the latter, how do I make an appointment, as I do not live in London so would have to make a special journey.