Blacklisted for a service cancelled last year

I gave notice for cancellation of my landline in Dec 2017, then again in Jan, Feb AND March 2018 as Telkom seems to have no record of it despite me forwarding the e-mails sent and having received e-mails from Telkom indicating that they had received my notification.

I am still being billed for the service despite having cancelled. I have contacted Telkom on multiple occassions and had the query "escalated" but still nothing!!! I have now been blacklisted for the outstanding subscription fees on the account despite not using the service and having served more than adequate notice. This is affecting my ability to access finance and needs to be attended to asap.