Forum staff should be able to sort it out, and they usually do.
Usually when this happens, things have gone wrong, the agent has agreed a contract with you that (although legally binding) isn't part of VM's desired "pricing pathway", and the organisation is trying to weasel out of the deal. It's not personal, it's not even deliberate or intentional, it's just what happens when you let Virgin Media run anything. We sometimes see staff here comment "you shouldn't have been offered that deal", but that's irrelevant, if a customer agrees a deal in response to written or verbal information, that becomes part of the contract. If you've already got the evidence of the PDF, then VM haven't got a leg to stand on.
Very occasionally there's some difficulty, and the forum staff won't sort it out. That's when we mention CRA 2015, and "Ombudsman Services".