Bad service with Telkom mobile

I am very disturbed with the service I have revived from telkom.

I had a contract with them in 2015 and only discovered that I have been put in arrears with them because I owe them, when I called them I was assured that instead telkom is the one owing me

When I requested for a settlement letter, at first, I was told to wait for 48 to 72 hours, a week later without receiving the letter I called and was informed to wait for 14 days and the consultant was very rude that they hung up on me.

How can my line not be suspended with them when I owe them? And why would I owe them when my contract was over in 2017 already.

I am utterly angry ?