AU Cell Phone Contract

Hello! My cell phone contract with AU will be expiring soon, and I need to get a new one. The problem is that I want to keep my old phone (an iPhone 4s). I tried going to a few AU shops in Tokyo but no one could really speak English (and my Japanese is not so good so I had a hard time explaining) and they were trying to sell me the new iPhone. Does anyone know any AU shops in Tokyo that have English staff so I can just make a new contract? Or, would it be best to buy a SIM card? I've never done that before so I'm not sure about it. I do plan on staying in Japan for a while. I really don't know what to do... Any help would be appreciated.

Typically your contract will automatically renew at the end of your initial contract period. So most likely you don't need to do anything all to keep your service.