I sold my car to We Buy Cars a while back and they had sold the vehicle to a customer and Cartrack insist that I continue paying a monthly premium for a service I don’t receive and I keep getting alerts on the vehicle

I sold my car to We Buy Cars a while back and they had sold the vehicle to a customer and Cartrack insist that I continue paying a monthly premium for a service I don’t receive and I keep getting alerts on the vehicle. I don’t believe this is right. I was told that if I can only pay a certain lump sum to avoid paying further monthly premiums.