If you have enough proof

If you have enough proof, for example, you have a contract with 人人传讯 that clearly states the 700min plan descriptions, you can look to the law to protect you. You can start with the local Better Business Bureau to file a formal complain, and then you can sue them at the Small Claims Court.

If you have written proof, then you'll have a very strong case. You can't just ignore this, if you ignore, they will continue to take advantage of other customers. You need to do the right thing.

Good luck!!