Debiting 2 policies for the same car for some months

I traded a car around March 2025 and somehow did not cancel my service plan. Around December 2025 I found out that the vehicle that I traded in, had recently been serviced using the policy that I did not cancel and was still paying for. When I requested for a refund I was told that it was an error as the person who bought my previous car also had a service plan and they just had to debit the funds for the new owner's policy. I was told that I am not entitled to any refund because I did not cancel my policy. They basically were debiting 2 policies for the same car for some months.