I have no idea why I have been charged twice $1.35 per month by Apple.com/bill

This Apple support Billing Article should answer your question.

Subscriptions and Billing - Official Apple Support

Also https://reportaproblem.apple.com

Also check Settings, your name, iCloud, Manage storage, change storage plan 

See this article about refund status

Check the status of a refund for apps or content that you bought from Apple - Apple Support

neira64 Said:

"I have no idea why I have been charged twice $1.35 per month by Apple.com/bill: Something that I didn’t used or any subscription but always charged every month by Apple?"

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Troubleshooting Purchased Subscriptions:

A. Verify this Cancellation:

• How to Cancel a Subscription from Apple - Apple Support
• Manage App Store Purchases, Subscriptions, settings, and Restrictions on iPhone - Apple Support

No Success?...

B. Contact Apple Support:

As you might suspect, no one here would know where this all stands. These are user-to-user forums, and no one here has access to your account info (and that is a good thing, BTW). So, contact Apple Support. They, run you through the fix.

Apple Support Contact Us Info:

• Contact Us - Choose Locations
• Proceed from there as necessary
• Note: Phone calls are taking a bit to go through at the moment, due do lots of calls. With the Coronavirus Pandemic, many are at home at the moment, with much time on their hands to contact Apple. So, just stay on the line, and you will get through :)