There's no provision in the T&C's for cancellation on basis of "poor service", it would be impossible to quantify that.
You should, at the very least, be following the complaints process which allows for referral to external arbitration - make yourself familiar with the process at https://www.virginmedia.com/legal/consumer-complaint-resolution-code-practice
The forum staff should be along in a day or so, and may be able to at least decipher what's going on. That said, it sounds as though your case potentially involves either a re-pull (new drop-cable from streetcab to home) and/or construction work.
Both of those scenarios are specialist and do require some planning - thus come with longer lead-times. They can also sometimes involve external contractors.