Unable to cancel service

Despite advertising that you can cancel your service with Afrihost at any time, this is virtually impossible! I have used Afrihost for my fiber service provider for over a year. In July I moved and contacted Afrihost regarding migrating my service. They were not able to assist as they do not cover the estate I moved to. I told them I would then have to cancel the service and stopped the payment from my side. I disconnected the router and moved from the premises on 30th July. They responded to my email saying I could only cancel online. I tried this but the website showed no connectivity service, so I thought it was cancelled. They then started sending emails and invoices showing my account was in arrears. I repeatedly responded that I was no longer using their services and had cancelled my account, but they repeatedly told me to cancel online. This has been going on for 3 months now and I have just received an invoice for October. They can see I have not used their services since July but I cannot cancel the services without settling the outstanding amount, which goes up and up each month because they refuse to cancel the account. Surely I am not obligated to pay for something I have not used and have cancelled repeatedly?