My car tracker contract

I joined car track at the beginning of this year , so I saw and ad ,felt like getting a tracker for my vehicle ,Requested a call back they called and they called as soon as possible , I waited for installation and until I went their Facebook page to get their attention finally it was installed ,paper work was done 3 months later I noticed money wasn't being deducted from my account ,I called them on a Saturday if I'm not mistaken the person I spoke to said they will escalate the matter to accounts , I waited for them to phone back eventually they did about a week or 2 ,we tried to set another debit order ,it wasn't successful again until I suggested to get another account to debit from ,she was said she will get back to me but I need to pay since i was now in arrears , last week I received a call saying I owe R2500 or less ,I was shocked I questioned how does R120 a month in months less than 6 ,she said it was interest ,and she said she will get more info for me and get back to me ,I'm still waiting .