still paying for Cancelled line

In March 2017 we app**** for a ADSL line and paid for the installation fee. In February 2018 after almost a YEAR of agitating hassle and frustrations with call centres, Telkom eventually came and installed the ADSL line. Unfortunately we could only have used it for 3 months. We relocated to a different town and according to Telkom there is no line in our neighbourhood that Is compatible with the line that we had. So as suggested by Telkom, we were told to rather cancel the ADSL line as they will not be able to transfer it for us. We went to the local Telkom shop to cancel the line. The lady there told us that sorry, they can’t cancel it in the shop we must please phone the call centre and cancel it telephonically. So we phoned the call centre and requested to cancel the ADSL line. We were then told that sorry, we can’t cancel it though the call centre we have to cancel it via the Telkom online app. We got the website details, and a step by step detailed form as to how to cancel it online. So we managed to cancel the ADSL line & our Land Line (Ref. Nr: ********** 7 & ********** 2) on 07 May 2018 @ 12:46. On 21 May 2018 we received a notification that both these case numbers has been resolved. BUT then the end of July we receive and Telkom Invoice saying that we are in arrears and we owe Telkom more that R1200.00. When phoning to follow up on this we were told that someone for the call centre tried phoning us to confirm the cancellation but apparently never got home of us. There was NO missed calls, NO messages and NO voice messages that ANYONE phoned us. THIS IS A LIE, WE DID WHAT WE WHERE TOLD AND STILL HAVE TO PAY FOR DOING THE RIGHT THING!!!!!!!!!!! Please can someone help sort this out. Im no sure what to do know as we are now being threaten with being black listed because we never paid the bill.