Two weeks of calling and waiting on someone to resolve simple issue

I canceled my Telkom fibre internet (40MB uncapped, R1260p/m) on 23rd of January and also received ref. (my id), and cancellation confirmation on the 25th of Jan that everything is going to be cancelled on the 28th of February. However, early in March I received another invoice for the amount of R414 for the current month, even though my internet was supposed to be cancelled completely.

Then I logged dispute ticket immediately (5th of March - ref. ********** 9) and was told that someone from accounts will come back to me. This was two weeks ago, so I phoned again today and found out that no one has looked at my dispute yet. Surprise. Also I was explained that this amount is for the part of internet related to the actual fiber line/port that someone from Telkom has forgot to cancel when canceling the whole package. This was canceled only on the 3rd of March, after system generated invoice was already sent to me.

Can someone please resolve this oversight and clear mistake on the Telkom side asap? I am getting very frustrated and impatient after two weeks of calling and waiting for something that is clearly Telkom's mistake.