They don't want to cancel

I had a contract of 36 months with this company from Sep 2021 till this year. I called in to find out if they would review my premium since I now own the tracking unit. They told me it will remain the same, so I requested the cancellation email address and I received it. In Aug requested them to change my banking details and they didn't do it. I then sent an email telling them that Sept 2024 premium was the last since the 36 months had ended and I will be cancelling on 24 Oct. I was paying in advance. So I sent a cancellation email which as usual they ignored and took my money. I reversed the debit order as I requested them to cancel. They have been harassing me with calls and messages demanding money from me, meanwhile they are still ignoring my emails which is proof that I requested a cancelation. I'm with another tracking company now and will definitely not pay 2 companies.