I am not able to cancel iCloud subscription

Cancel upgraded iCloud storage by downgrading to the free 5GB plan. See instructions in the following Apple article: Downgrade or cancel your iCloud+ plan - Apple Support

If needed, note the following from those instructions:

If you can't tap Done, make sure that you're signed in with the same Apple ID that you use for your iCloud+ plan. You can also try following these steps on a different device. If you still need help, contact Apple Support.

uttara162 Said:

"I am not able to cancel iCloud subscription"

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Properly Downgrading iCloud:

1. Download All of iCloud, First:

Prior to downgrading, download all of iCloud. That way you do not lose any data, once downgrading.. Use my user tip: Getting a Quick and Direct "iCloud Drive-to-External Hard Drive" Download - User Tip

then...

2. Downgrade your iCloud Plan:

If you want to get less storage in iCloud, downgrading your iCloud plan is the way to go. Note that this has a monthly fee. Here is the link to user: iCloud+ Plans and Pricing - Apple Support. Note that this service is not available in all countries/regions.

You are not able to contact Apple Support? What happens when you click on:

If you still need help, contact Apple Support.