Edgars ruined my credit score

I paid off and closed my account in 2015. In 2016 I kept getting sms's and calls that I had amounts due on my account. I went to Edgars Centurion and to my surprise i was told there is a cellphone insurance that was not cancelled when closed the account. After months of back and forth with Edgars I decided to pay off the amount, and while at the the shop, we called the insurance to cancel.

Can you have Edgars cellphone insurance without an Edgars account? No! Can you walk in and apply for insurance without an Edgars account? No! How come i got billed for insurance if the account was closed? Now October 2018, on my Trans Union Credit score report shows I have a default payment with Edgars. Called the call centre and they told me that the system shows the call i made and the last payment in 2016 but from then till now this account was not closed. On the report it shows that Edgars just decided to write off the amount in January 2018 but still shows unpaid on my report. I called customer services and they referred me to collections and they referred me back to customer services which did not solve the issue, was put on hold for over 40 minutes.