Matrix car tracker

Good day,

Kindly help , I had registered my car tracker in 2017 with Matrix, in 2020 I downgraded as I was paying lot of premium, now I want to cancel the car tracker they are telling me that I can't cancel because I have 36 months contract with them. I requested the contract or telephone agreement no one is responding the payment rejected last month as they debited on 24 while I had agreement with them to debit on the 25 .as I cancelled in May over the phone no one said it should be in writing after sending in writing all the statements come up I don't have written contract or policy sent to me yet they are threatening me to record me on credit bureau as a bad person .