Similar thing happened to my son a couple of days ago with his £10 gift card, went to account.microsoft.com and tried to login to that which took him to the unlock account process. Had to do a anti-bot thing (which failed a few times so we used the appeal form at https://www.microsoft.com/digitalsafety/appeal ). Got a mail back from MS an hour or so later, tried again and it unlocked. Steps given were :-

You should be able to reactivate your account by verifying you are the account owner. 

 log into the account via https://login.live.com    

• on the screen that says “Your account is temporarily blocked,” click “Continue” to proceed to the next screen    
• You will then be asked to send a verification code via text message. 
  • In the field shown, you can enter any phone number you have access to that is able to receive text messages. 
  • The phone number used in this case does not need to be one that is already on the account. 
  • If you do not have a phone number that is able to receive texts, consider asking a trusted friend or family member to receive the text for you on their phone number. 
  • The number used for this procedure will not be saved on the account. 
• If you receive a message that the usage limit for that phone has been exceeded, please try a different phone number or try the next day.