defective device but still require cancellation fee

good day , I recently bought a vehicle in February and contacted secure drive to have a tracker fitted on the vehicle the device only worked for 3 days , then stopped working , I have contacted them several times about the device not working but 2 weeks later I have not been assisted now I want to cancel the contract and they say I must pay a cancellation fee , mind you the only reason I am cancelling the service is because the device is not working and that negatively affects my insurance , they said they would have someone call me in regards to the cancellation but that hasn't happened yet. how is it possible that I have to pay for there incompetence all this is happening now from the 11th of February 2025 to now March 5th 2025 , I'm getting no assistance from them yet I have to pay for a cancellation fee ?