Thanks for reaching out to the Apple Support Community. I understand you are having trouble with managing your subscriptions, and I have some information that may help. You can manage your subscriptions from your computer as well, using the article below.
View, change, or cancel your subscriptions - Apple Support
If you would prefer to resolve things form your iPhone, it can be helpful to sign out of the iTunes & App Store. Keep in mind that if you are an Apple Music member, your songs that are downloaded for offline listening will be removed when you sign out. You'll need to download them again once you sign back in. Just as a heads up, if you have downloaded any songs from Apple Music for offline listening, you will need to redownload them after signing back in.
To sign out, follow the steps below:
1 - Tap Settings > iTunes and App Store
2 - Tap your Apple ID
3 - Select “Sign out”
4 - Restart your device
5 - Sign back into the same settings
If the behavior persists or you run into any trouble, we're here to help.
Best Regards.