Wrong amount been charged and horrible service

I took out the security in June because a guy by the name of Edgar, came home and told us that Chubb is running a special, which is R190 a month with the first two months free and this includes fee instillation. I asked him before I took the contract that in august would I pay only R190, he rep**** yes, I had other people present when he said that. at the end of august they bill me R537, I called to find out why, they said that subscription is R330 and not R190 and I had other charges. I tried to call the multiple time to sort this issue out because I will not pay R330, all they say is we will get back to you, I told them I don't not want the alarm anymore but no one has gotten back to me and its been 2 months, plus they are still billing me. I want someone to get back to me now and sort this issue out now and not say they are going to get back to me. I been waiting two months for them to get back to me.