Account issue

Last month I was charged R1018 for my subscription that is supposed to be R519. I logged on to self service to see what was going on and saw that it shows i have 2 decoders and 2 different subscriptions which I don't have! I went into dstv to find out what was going on. The service consultant then wants to tell my I probably activated the service it by accident. How do I activate something I don't even have? After that I was told it's a mistake on their side and my account will be credited for the overcharged amount and they will deactivate the wrong decoder. I later logged into my account again to see if it was done. Now my account says my next payment is R336.44. How do you get to that amount? R1018 - R519 = R499!! I owe you R20 for next month if you charge in advance! Fix your mistakes!