I think that I have had something like this happen to me just now.
In a slightly more sinister way, I called to cancel my contract as I was then out of contract. I was informed of when my contract would end and my final bill. I have just found out now that I have been entered into a new 18-month contract without my consent. I've been paying them fro the last few months, didn't notice.
It's more of a pain as I have a contract with a new web provider and don't need Virgin Media anymore. I just spent a good hour on the phone complaining. I should receive a call from the manager of the agent who put me into the contract in the next 5 days. My complaint about this at the moment is inconclusive. Though I want to hear the phone call of me saying yes to the contract extension, something I know that they don't have.
It's frustrating as I was with Virgin for 10 years without an issue, so it does leave a bit of a bad taste in my mouth.
[MOD EDIT: Post split to create own thread. @FrazerG please add more details so the Community can help]