paid tracker, but no tracker installed.

You know 6 months ago when I got my car I was billed R4999 for a 36 months pre paid tracker, yesterday when I was trying to track the car it turns out the tracker was never installed, apparently they were supposed to call me within few days to have it instlled but they never did, so ive been driving a car for 6 months thinking ive a tracker on the car but nothing, yet Iwas billed for it. Now they say I must come have it installed on monday, should I take the matter lying down or?