Cancelling Apple TV+

I was given a one year free subscription to Apple TV+ when I took out a broadband contract with Vodafone nearly a year ago. I didn't want it but it came as part of the package and they said you can cancel it before the end of the 12 months. I followed the instructions for cancelling in the Apple TV+ app but it says I don't have a subscription (so logically I can't cancel it). How do I ensure they don't start charging me on the 366th day after the free subscription started? Can anyone advise please?