Debit order mandate not being removed

They had phoned me when I had bought my car, offered me some insurance options. I agreed to one on the phone. After doing some extensive research I opted out, because I found I had way better options elsewhere, I contacted them to let them know I want to cancel and they took over 10days to get it done on their side. Now the continue to try and debit me 850 for their services which I don’t use, I had sent an email to stop the mandate and they still ignore it and continue to debit. I want to cut ties with them completely. No one has contacted me about this and I want to be removed from their client list since I literally don’t use their products or their services but they still charge me.