Hi Rafael,
Do you have access to the portal? If yes you can use below instructions to create case and have support call you back. Using my instructions many people have been successful opening a case and having support contact them about billing issue.
Use this link to start the process:
https://portal.azure.com/#view/Microsoft_Azure_CostManagement/Menu/~/support/openedBy/AzurePortal
Fill out Summary, Problem type, Problem subtype, click Next. There will be a delay, then some recommended solutions will be shown. Do not click on any of the recommended options shown.
In the upper left corner, click Return to support request
Click Next to move to Additional details tab, fill out required information, email/phone, etc., click Next, review details and submit case. Make sure you select the option for them to contact you via phone if that is what you prefer. After submitting you should receive an automated email within a few minutes and a support engineer should contact you within 1 business day.
Please click Accept Answer and upvote if the above was useful.
Thanks.
-TP