How do I find my Apple Icloud storage subscription number?

There is no account number. As said, the Subscription is tied to your Apple ID.

when you subscribe you get an order number for the first payment, and you get other order numbers for subsequent payments. There is no unique account number.

What do you need a number? What are you trying to accomplish with that number exactly?

What number? The iCloud storage subscription has no number. It's tied to your Apple ID.

What exactly are you trying to accomplish?

Check -> Go to -> Settings -> your name -> iCloud -> if you see 50 GB (or 200 GB ot 2 TB), you will receive a monthly bill from Apple, check your e-mail box.

You pay monthly for iCloud storage.

The iCloud + subscription will be terminated depending on the start date.

If you start on August 1 and are going to cancel now, the subscription will stop on November 1.

a monthly term is used.

On the invoice you will see: your Apple ID, Billing date, Order ID, Tracking number & Document number.

Have you check your mail box & find the invoice?