Return not collected and calls not answered

I received a call from Sell Direct on behalf of Telkom letting me know that my contract is due for an upgrade, they offered me a wifi router with additional data for the same amount that I was paying, I agreed to upgrade the contract and accepted their offer. Once the router was delivered to myself I saw Telkom's November Big Deal, which was more cost effective to my upgrade with them. The same day that the router was delivered I decided to call them and ask to cancel as it was still within the cooling off period. I called Telkom to cancel the contract, thinking it was taken with them, only to be told that I need to contact Sell Direct as the contract was taken with them. After hours of calling and calling I eventually got through and was assured that the contact would be cancelled and that the courier would collect the device as it had not even been opened yet. This all happened on the 1st of November 2017 and to date I am unable to get through to the call center as the device has not been collected yet and I do not want to be billed for something I haven't even used.