You're using the term "wifi" as though that's what VM supply. In fact that's the one thing they don't supply - they supply a broadband (and possibly TV/phone) package, and a hub that's capable of providing wifi, which is that last few metres between the hub and wireless devices. As VM would normally brush off wifi complaints as not their problem, I'm guessing you mean you have an unreliable broadband connection? If you are, the following comments apply.
Under the Fairness Commitments that Ofcom drew up and VM signed back in 2019, they agreed with the regulator that customers could leave fixed term contracts without penalty where the company could not resolve problems in a reasonable time scale. As with most of the rest of the commitments, VM don't bother themselves too much with complying with the details. You're also entitled to leave a services contract without penalty if there are problems that can reasonably be argued to show that the provider has not delivered the service with reasonable care and skill (Consumer Rights Act 2015). You're also entitled to compensation for the protracted nature of the problem and poor customer service, perhaps around £200, based on my reading of the adjudicators guide for compensation. In your situation, I think that if the problems have been going on for an unreasonably long time, since VM have had multiple efforts to resolve the matter then agreeing cancellation without penalty and compensation is an entirely appropriate outcome. This forum is perhaps VM's last chance saloon before you take the matter to the industry complaints adjudicator, CISAS.
If you can clarify whether this is broadband or wifi that'll help us give the most suitable advice, and you can also see if the forum staff (who have some visibility to the contacts you've had with VM already) will arrange an agreeable settlement before I explain the process by which a complaint can be taken to CISAS.
