Car Track charging and Cancellation Fee for Vehicle that is no longer owned by Myself

i have a contract with CarTrack on a tracking Unit on my car that has just been Sold

i called Car Track now to cancel the Contract and they are telling me that i need to pay a Cancellation Fee

i no longer own the Vehicle and they want to Charge me a a Fee of Close to a R1000

This is Quite unfair as i do not own the Vehicle Reg : HW83TTGP