Hi Carlos,
Welcome to Q&A Forum; this is a great place to get support, answers, and tips.
Thank you for posting your question; I'll be more than glad to help you out.
As this is (mostly) a community-driven forum or most of the answers are from community members and not an official service desk, most of us won't be able to clarify this... you have to open a support ticket.
Where did you get those notifications? In the Azure portal or via mail?
BUT from my experience and my stomach... this sounds like a phishing attack... if you checked all of your assigned subscriptions for open payments/bills...
https://portal.azure.com/#view/Microsoft_Azure_Billing/SubscriptionsBlade
or if you open up the details of each of your subscriptions and click on billing - invoices, you should be able to see where an open balance is.
I hope my answer is helpful to you,
Your
Bjoern Peters
If the reply was helpful, please upvote and/or accept it as an answer, as this helps others in the community with similar questions. Thanks!