Subscriptions
I have been charged for two months with the tidal app, however when I open the app it says I am not subscribed as well as in my subscriptions in my settings it says the subscription which was a free trial ended jul 20 of this year.
If it isn't showing in your subscriptions then you may have subscribed directly with Tidal, check with them.
If it does show that you are being charged by Apple: iTunes Store - Contact Us - Apple Support
Subscriptions