Dear Montse Espejel,
Good day! Thank you for posting to the Microsoft Community.
I'm sorry to hear that you've having issues accessing your account due to authentication. May I please know the type of account you are using? Is it an M365 work/school account or a Microsoft/Personal account like Hotmail/outlook.com?
Since you posted in the business category, you may need to contact your organization's M365/IT administrator to reset MFA for you through the Azure admin portal. In the Azure portal, the administrator can set their account to Require new MFA registration. This disables all authentication methods and deletes the old phone. You will then be prompted to configure a new MFA authentication method the next time you sign in so that you can do the set up afresh and add the new phone. The admin can also add another verification method like Phone/SMS for you.
More info at: Manage authentication methods for Azure AD Multi-Factor Authentication - Microsoft Sign In | Learn with Microsoft
Thank you for your kind understanding and have a great day.
Best regards,
Ashraf.