billed for a cancelled contract

I was offered a contract for R199 a month which I accepted on condition that there would be sufficient LTE coverage in my area. I received the modem and SIM card and thereafter I had to wait 48 hours for activation, unfortunately the signal quality was poor and even connecting was a problem. Within the seven day period I returned the device and cancelled the contract, the modem was promptly collected by RAM couriers within the seven day period and returned to Mobile Talk. I was then billed R150.00 which came off my account on the 25th of Jan, I contacted mobile Talk on the 1st of Feb, they apologised and said the funds would be reversed due to the fact that I cancelled the contract within the seven day period. This money was never reversed and now I have been debited again for R340.33 on the 25th of Feb for a product I don't even have in my possession. Please make the necessary arrangements to reverse these charges and ensure that no further monies are debited off my account asap