Unauthorized debit orders

I had a worse experience of my life with Cartrack,I got a debit for my instalment and 2 extra debits that were times 3 of my instalment and I disputed those transactions because they were suspicious and after the dispute I got the call from the consultant and I was told that my account was on arrears,I told them that the transaction went through instead I got debited 3 times and I was told that it was for subscription of which it didn't make sense because I have been their client for about 3 years,this happened around Feb,at the end of August I received a call from one of their consultant and apologised regarding the transaction that had been happening on my account and she said my account is up to date I'm not on arrears,month end of August I got debited of my instalment and the transaction went through,I received a call on Tuesday 10 September from their consultant saying that my debit returned as unpaid where as on my banking app and banking statement it has gone through,i explained to the lady that lately i've been experiencing this with their company i requested to cancel and i was transferred to the lady by the name of Nontobeko,who assisted me to cancel of which i did,same day just after cancellation i received a message that said i'm going to get a call regarding a tracker installation for my car and now they are harassing me with emails i received 6 emails on 1 day stating that my account is on arrears and this is after i had cancel my contract with them.