Megane Diamonique Radio Code help needed

I need help with radio code on my megane Diamonique. Taken the car to the garage to get the ITV (MOT) done and a full service. Car came back and because they had disconnected the battery the code needed to be put in again for the radio. One small problem, the code that I have that I have used before does not now work. So I have no radio as the dash simply says code. Is there a way to reset it back to factory settings so that I can put a new code in again so I can get the radio/CDs playing again. All worked fine until the garage. HELP!!!! :-) Thank you in advance