Well, as you probably know, VM owe you compensation for the delay in installing under Ofcom's rules that you can read here in full, at the rate of £5.25 a day (daily rate updated from the full guidance as per this web page) from the first promised date through to thirty days after they issue a formal "cease notice". A cease notice is not the same as just cancelling the contract, it's a formal notice that they do not intend to keep paying the automatic compensation. Have you seen such a notice? Thought not, in which case the clock keeps ticking, and then there's the thirty days extra as per the Ofcom rules as soon as they do. If VM contest the amount of auto compensation you are due, be aware of this issue.
See if the forum staff can sort this all out for you. If they can't or won't, raise a formal written complaint* posted recorded delivery to VM (address on this page) demanding that they pay you the full amount you're requesting. If that gets the right outcome then job done. If that gets fobbed off or they don't pay you both everything you're owed and the compo, you reply rejecting any "resolution" they offer, asking for a deadlock letter, and with the deadlock letter you ask CISAS to resolve the matter, including additional compensation of say £70 for the subsequent poor complaint handling.
* Ignore the telephone, chat and web forms for complaints. The telephone and Whatsapp staff are poorly trained and don't understand (any) Ofcom regulations, and the web form hasn't been working reliably for over two months now. Meanwhile VM management are saying "Wow, complaints are well down, aren't we doing a great job?"
