When you sign up for VM, VM checks to see if there has been a connection at the address before. If there has been, VM sends you the 'Quick Start' equipment for you to plug in yourself.
VM does not know if the cable at the address is working or not, just that there has been a past connection.
Once VM sends out the equipment, VM deems the service to have been 'activated' and starts charging you from a few days after delivery. If VM has started charging you, and you have not paid, that is why you are being contacted by debt collectors. All of these processes are automated and any human intervention in the process is simply not there.
If you have found there was no cable, you need to request a technician visit to install the cable by calling the pre-installation and delivery team on 0800 052 1734.
If you run into a problem with a 'Quick Start' installation VM classes this as a fault. Once you have notified them of the issue by phoning them, you should become eligible for compensation as if you had a fault as per
https://www.virginmedia.com/help/billing-and-payments/automatic-compensation
the day rate for the last financial year was £9.33 per day.
If you told VM you wanted to cancel within 14 days of receiving your equipment (by phoning in, post or returning the cancellation form which came with the equipment) you should have been able to leave without penalty.
If you have told VM you have additional communication needs, which makes phoning difficult, VM should make reasonable adjustments for you.
Sounds like this has all escalated into something of an admin muddle and I doubt the regular support channels of VM will be able to sort it out. You may have more luck with the VM forum team on here.
I would also imagine that VM could well have logged credit defaults against you if they have passed on the perceived debt to a debt collection agency. You may want to check your credit record to see if this has happened.
Keep some very detailed records (including dates, times and evidence) of when all of these things happened as you may well need this going forward.
Would suggest that you follow up a PM with the VM forum team person on here to try to resolve this.