Cartrack agent failed me here

My car was bumped last year, yet that time i wasn't working. So now after sometime they call me asking about the money for tracker i did tell the guy who called me that i still need to fix somethings and i will continue paying. after two months three i got another call saying i am blacklisted i must pay 1800 cash to be removed from bureau credit. I was so amazed cause i thot the agent who called me did put notes on my file so now am stuck on this thing and am willing to pay that 1800 but not cash cause my life is still having difficulties. They failed me by not informing that i can change my monthly instalment for the time fixing my car