They refused to cancel my contract

I sent a cancellation letter to Ashmeera Kiren in July 2014, but she refused to cancel my contract saying I should pay a cancellation fee first for the amount of R1710 I told her I cannot afford to pay that amount all at once but she insisted they want the whole amount at once, the contract continued and last month I received a call saying I am owing Chubb R4370 and I explained to the guy that I tried to terminate their service since I have relocated to Johannesburg and no longer need their services with no success and he said if I did sent a cancellation letter they were suppose to cancel so that the monthly instalments would stop and only owe Chubb the cancellation fee now it has accumulated to R4370 because there is no proof that I sent a cancellation letter and when I call Ashmeera she agrees that she does have a cancellation letter that I sent but she could not proceed with it before she receives the money. This morning I sent another cancellation letter to their Head Office and she is the one who sent me a letter confirming the cancellation but still I must pay them R4370 & R1710 for cancellation, I have not yet paid the cancellation but she managed to cancel this time