Double billing

I got a message from Multichoice/DSTV two days ago about the outstanding bill that i have to pay, and i was suprice as last month during the easter weekend i just paid - R350 for monthly fee and reconnection, and now i got smsm saying i owe R974.20. Then i called the call centre and i was told i was billed for two decorders and the other was activated on the 4th. I do not have two decoders and two smart cards, and i fail to understand how do i now have to pay another account i did not request. I have spend enough airtime calling the call centre, and they dont seem to to find a way to help me. I am not prepared to spend more than my monthly premium to sort this. Hope some pick this up and do something about it.