cartrack can live up to 150000 garantee

i had an cartrack unit in stalled witch was fine until the 3 year contract was finished now acorrding to the contract they will install and maintain and monitor the tracker unit and after the 3 years the unit will be my property and ill only pay for the monitoring of the unit wich is fine but now they want me to pay 300 rand a year to keep there garantee of 150000 they'll pay if my car is ****** and they cant track it so first that wasnt the deal and second why must i pay them to keep their garantee they have to garantee their product free of charge