no longer have an iphone

Depending on what subscriptions are involved you may be able to cancel them by logging in to https://tv.apple.com or https://music.apple.com with the Apple ID that holds the subscriptions, and click on the Profile icon at the top right corner.

For other non-Apple subscriptions, you will need to use an Apple device or computer (Mac or PC) logged in with your Apple ID to cancel them. You can use iTunes on a Windows Computer for this.

click here ➜ If you want to cancel a subscription from Apple - Apple Support

and here ➜ How to cancel Apple TV+ - Apple Support

PS:

Melpetersen..

While other ideas may work, given you've

no longer Apple devices in your possession

..this was something to see if it'd work out:

"Remove a payment method online" (this is an Active link)

You can also remove a payment method after signing in to appleid.apple.com.

[.In some countries and regions, you might need to add a new payment method

using appleid.apple.com in order to remove the existing payment method.]

Remove a payment method from your Apple ID - Apple Support

Note: the Link will work when clicked and opens login to Apple ID control site.

Perhaps this article may suggest route to remove payments

from your Apple ID account; seems it does say something..

If you need to change or update your Apple ID payment method - Apple Support

//support.apple.com/en-us/HT213276

Also you may login to Apple ID with web browser

and change settings without an Apple device.