I typically CALL customer service when I want to make changes to my plan or when my balance hits zero and I need to figure how much I owe. This came in especially handy when I arrived at PVG in March after 3+ months absence; the WiFi wasn't working at the time, so I needed data just to be able to pay them. The lady on the phone turned my service back on for 72 hours. You can always reach customer service (real people to boot) from within China, even when your account is locked. IMO this is much better than going to the store because the CS people can see all details about your plan as soon as they connect, and you don't have to bother finding a store, let alone wasting an hour plus waiting in a store.