I want to cancel the added icloud storage effective immediately

Cancel upgraded iCloud storage by downgrading to the free 5GB plan. See instructions in: https://support.apple.com/en-us/HT207594

Also note the following from that support document:

If you downgrade or cancel your plan, the storage change takes effect after your current subscription billing period ends.* 

and

* Partial refunds are available where required by law. If you recently changed your iCloud storage plan, contact Apple within 14 days for a refund. Learn how to request a refund.