How do I delink my mobile number with an Apple Account?

StarStasya wrote:

I want to disconnect my mobile number with another account

I’m assuming both Apple Accounts here are not yours.

Contact Apple Support, and explain the particular Apple Account and phone number issue to them: Contact Apple Support - Apple Support

So your friend has associated your phone number with their account somehow, and is unwilling to change that?

And whatever the account setting might be, Apple is unwilling or unable to alter that?

Seems you’re left to negotiate with the friend directly, or to pursue whatever legal recourse might be available, or to change the phone number, then.

If the individual with the Apple Account configured to bill your mobile without permission cannot resolve this within their Apple Account configuration using the following:

• Add a payment method to your Apple Account - Apple Support

Then notify your cellular provider and notify local police.

Contact your carrier, and inform them of this fraud.

Billing without permission is fraud. Call the police. Maybe your friend then remembers how to not bill your account.