Howdy, so the previous owner of my phone number linked it to their Microsoft.

Hello, and welcome to the Xbox Community! I'd be happy to help you today.

If it was registered into another account, you won't be able to use it. That's the issue with carriers recycling numbers.

Phone numbers are treated as security credentials, not just contact info. Microsoft won't let two accounts verify the same phone number at once. That’s by design. It's a defense against hijacking and recycled number attacks.

You may try to recover your account using a phone number through this link https://account.live.com/username/recover

Just make sure that the phone number was added to your previous account or was part of your account alias.

I also tried to fill in my phone number instead of the old mail address, but then I only happen to change the password for another more recent Microsoft account that is also linked to my phone number.

The 30 day lock down period is a security measure implemented on one account. Since you are unable to verify ownership by entering a verification code sent to the original phone number attached on the account, the system applied the lock down so if there
is any chance, for example, that you are not the account owner, the real owner will be able to revert back the changes since he has access on the original phone number attached to it.

Codes are one time use

Also.it would.be linked to the previous owners. Battlenet acocunt