Unfair Business Practice - Incorrect Billing

I've paid my dstv account correctly and have never been in arrears. Suddenly, I received an email from dstv informing me that my decoder insurance is in arrears. I have submitted a dispute and await your response. Now you are saying my dstv account is in arrears. I called your call centre and spoke to Nhlanhla, I was on the phone for 21 minutes, my query was not resolved until I ran out of airtime and he didn't bother to call me back. What I also find find strange is that my sister in law is on the same package as me but she is paying way less than me, how is that possible? Please contact me with feedback on the decoder insurance query and also an explanation of the arrears on the account which I don't understand and I am disputing.