Telkom Speedlink - unable to cancel

We closed our practice end May 2016, Prior to closure we cancelled all Telkom accounts -Telephone, Fax, ADSL, Mailbox and Speedlink Services, at Telkom in Tygervalley Centre. Now , after 25 months, we are pestered by a debt collection firm about outstanding amount for the Speedlink service.( account from June 2016 - June 2018) We have not used Speedlink as we are no longer at that location This is the first contact with us about this account All the other services were cancelled as requested, but clearly Telkom did not cancel the Speedlink account . I notice there are other customers with similar complaints. I find this totally unacceptable. AMT