Harrasment and ******ion

I had a contract with mix telematics since 2018 January, about 5 months ago they called telling me my device is offline and my contract has expired. I told them to just cancel my contract as it has already expired and not bother fixing the device... My request has fallen over many deaf ears because I keep getting calls from them telling me about my device being offline. I keep telling them to cancel, today they called again. When I tell them to refer to previous calls and cancel then suddenly there is a cancellation fee. The consultant even hung up on me as I was asking questions.