Light after 3mmths of darkness!!

I have been trying to resolve or atleast get an explanation regarding this matter for the past three months to no avail what so ever. In the month of June 2016 I called into the call centre to cancel one of my lines as it was due to expire. At the time I had just become a pensioner i advised the consultant that i can no longer afford the contract, so i figured cancellation would therefore be my best option. Then i was offered a great top-up deal whereby i would receive an amount of 1GB data for the cost effective price of R20 per month. Obviously being a pensioner i found the offer to fit my budget and expenses affordable. I accepted the offer. Without problems i paid the monthly amount and received my data, like clock-work.

Until June 2017 my line would continuously be disconnected until i call the call centre and explain the story my line then gets opended. Until i was told that my account is 60days overdue with an amount of R340.

Now i need help with trying to understand how a simple top-up can incure these charges seemingly out of the blue??? I keep being sent from pillar to post with nobody even attempting to explain what exactly happened. Or where the misunderstanding came into affect. With all this time that has passed its obvious that this would impact negatively against my name.

Some clarity would really be appreciated regarding this matter.