NOT HAPPY WITH MATRIX

i have been trying to contact this company's customer service, accounts department,app department and debtors department by emails and phone calls with no success, they charged me the amount which was not on the agreement which is R169 per month, they installed the unit on my car on the 7th September and before i agreed to it i asked the sales person if they will charge me prorata and he said no because it is the beginning of the month but now it is appearing on September invoice and the amount is twice the initial agreement. they charged me some of the things i was not made aware of and now when i try to call them no answer and when i send emails they just ignoring them so i decided not to pay until they contact me and clarify this issue and i am even considering to cancel this whole agreement.