Permanent Cancellation Of My Fitfy App Subscription From Apple Store

I am using the Fitfy mobile application with a subscription purchased through the Apple App Store. On May 7, I attempted to cancel my subscription, but despite this, the cancellation did not go through and the subscription still appears as active. Since May 8, my card has started to be declined in connection with this ongoing Fitfy subscription, and I am unable to use my payment method properly. I have not yet contacted Fitfy support or Apple support, but I would like this problem to be resolved as soon as possible. I request that my Fitfy subscription be immediately and definitively cancelled through the Apple App Store and that any blocks or effects on my card due to this subscription be removed so that I can use my card without issues. I also expect written confirmation that the subscription has been cancelled and that I will not be charged in the future.