I need to cancel the iCloud subscription since I cannot downgrade and do not wish to pay any more

This page gives you details of how to downgrade on various platforms:

Downgrade or cancel your iCloud storage plan - Apple Support

Should you still have trouble there is a link to contact Support.

Hi there!

Downgrade or cancel on your iPhone, iPad, or iPod touch.

1. Go to Settings > [your name] > iCloud > Manage Storage or iCloud Storage.
2. Tap Change Storage Plan.
3. Tap Downgrade Options and enter your Apple ID password.
4. Choose a different plan.
5. Tap Done.