Charged double

I have an account with DSTV, been paying the same amount for one subscription, for some reasons I am being charged for two decoders, one that I don’t use and doesn’t exist and the one that I am using, I called, I was told that the decider has been active from May, but I didn’t pay for it?? To my surprise now I must pay for something I haven’t watched, nor used…. What bogus is this ??? Call Centre agents have no sympathy at all or customer service