Need help with contract cancellation and bill refund.

I had cancelled a contract with Vodacom on the 19 July 2017 which was two weeks after they delivered the Smart tab device to me,i requested them to collect it back which they did after 3 months of a numerous calls begging to come and collect and by help from Hellopeter,however even after they collected the device and confirmed to escalate the cancellation issue to their accounts departments Vodacom is still billing me for the contract that i have never used,everytime i call them they say it will be escalated i will get comfirmation and my money will be refunded.My reference number when i started calling on 19 July 2017 was 3369 everytime i get a new reference number ,on the 04 Aug 2017 i got ref number ********** 652,on the 16 Nov 2017 i got ref number 1- ********** ********** to day 11 Jan 2017 i got ref 1- ********** 710.I am so sick of Vodacom i dont what to do anymore ,i need help please.