Defeated!

I have complained multiple times to multichoice about bring over charged. When I opted to take the R500 black friday special last year December I didnt know it would cause me so much stress. An agent doubled my application and I had 2 decoders delivered to my door. Ofcourse the second one i sent back because there was no need for it, since January I've been paying for both. Spoke to a lady that assisted with this dispute in March, she passed credits on my account to make up for the extra amounts I've been paying. I assumed my issue was resolved. To my surprise a month later I was being billed R793 again. Stil no resolution.