Subscription cancellation

I was involved in an accident and they did not ask me if the car is still operational. The car is no longer in my possession however they are still deducting the monthly subscription - which needs me to always go to the bank every time they deduct. They want me to cancel the contract and serve a notice. How does one serve a notice for something they no longer have? It does not make sense. They want me to, in that notice to continue paying for a service I no longer need. They keep harassing me with calls and it is frustrating.