Frustrated and dissapointed Client

I signed up for 50 GB wifi with Telkom and then after sometime they advertised the unlimited one for 899 so I went back to the shop at Mall of Africa to ask them to upgrade mw to the Unlimited, good enough I signed all documentation and guess what end of the month I was billed for both the 50GB and the Unlimited, which I paid and the next month and the next I have been going from pillar to post trying to rectify this to no luck, I went back to Mall of Africa and requested to cancel everything since this was just a n=mess I signed the cancellation forms twice and believe you me nothing has been done and am since getting charged for both devices I was told to take them back to the shop and when I got there they didn't want to take them and said I have already paid for them so they are mine, but the people at their Cape Town office phoned me to say I must return them, I told them I don't have time to waste since I had been to the store 3 times trying to return these, I stopped the last debit order for R 1700 last month and this month I got a bill for R 3777.00 I do not know who to speak to get this solved, I love their unlimited WIFI and with the being charged double for 50GB and Unlimited I think its best to cancel both, I just feel nobody takes you serious a client once you out down the phone its done.