3 Months of *********** Billing

In February I received a massive bill from Telkom. Upon investigating I realised I was being charged for someone else's line and usage. I reported it to Telkom and was told my account would be credited. In March I was billed for the same incorrect line again. I raised it again. I was only given a partial credit this time. I raised the problem again. This month (3rd in a row) I am billed for the incorrect line again. This time with interest for unpaid charges. So now I have to talk to billing again. Can't Telkom just fix the billing the first time? Why do I have to keep telling you its a mistake for your *********** staff to just make the same mistake over and over?