Unhappy customer

my contract expired end of August but in February I was offered a migration but there would be no change to my expiry date. Now they have added an extra 6 months onto my contract saying the expiry date is now February 2020. After numerous calls and promises to investigate I am still waiting for this to be rectified in order for me to cancel as they have confirmed telephonically that they have made a mistake. Not a happy person at all as these big corporations think they can do as they please.