If you are within the 14 days since the date you took out the contract you can cancel. If not, then the only way would be to make an official complaint and demand that Virgin pull the call and it is listened too. If they still don't listen take it further should you need to do so.

Are you paying by direct debit. If not is the £9 per month only if you pay by direct debit?

Even though you have only verbally agreed over the phone, as far as I am aware you have consented to the 12 month contract.

If I am wrong then I hold my hands up, but as far as I know.