These "didn't get the deal I agreed" situations happen from time to time. However, your legal rights are crystal clear - information provided by a company verbally or written is binding if the consumer relies upon it when entering a contract (Consumer Rights Act 2015), so VM have to honour whatever was promised, whether they like it or not. And perhaps they need to re-train some of their staff.
Hopefully the forum staff can pick this up and get it sorted - by which I mean that you get exactly the deal you were promised, not some less attractive compromise. That would be the cheapest and quickest resolution for both parties, and the best way of trying to recover some goodwill in a bad situation. If they can't get it sorted in that complete manner, you need to search, read and follow the Virgin Media Complaints Code of Practice. Don't start a complaint until you've seen if the forum staff can get this sorted, because I believe they can't get involved once it has become a formal complaint.
If you do need to raise a formal complaint (I suggest in writing, by recorded post), reject the contract they're trying to impose, and demanding that as per your legal rights the company honour what was promised, and pointing out that if the company can't honour its agreement you will escalate to the industry arbitration scheme CISAS as soon as permitted by the rules. In the meanwhile, don't do anything daft like stopping your direct debit, that'll be recorded as a credit default, and opens up whole new realms of difficulty for you. Don't worry if VM contact you claiming that they couldn't get hold of you, so will close the complaint if they don't hear to the contrary, this doesn't stop you being able to take the matter further.
If VM still won't honour the contract despite the complaint, or say they're going to close the complaint, then you follow the process and escalate to the industry arbitration scheme no sooner than eight weeks after your initial complaint was received by VM. Explain the background and request that VM be required to give you the promised deal, fully backdated, and add on a request for compensation for the hassle. Not only does escalation to CISAS cost VM money (free to you, costs of several hundred quid are ALWAYS paid by the company) but it gets your case investigated and impartially heard by expert dispute resolution staff. From published data, the majority of complaints escalated to CISAS, either the company immediately concedes, compromises, or loses at the end of arbitration. Sadly that's not quick, and VM have up to eight weeks to resolve the complaint before you can go to CISAS, on the other hand your legal rights are very clear.
Fingers crossed for both you and VM that the forum staff can get this resolved quicker, cheaper and without the formality.
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