I would recommend you initially respond thus: https://learn.microsoft.com/en-us/defender-office-365/responding-to-a-compromised-email-account?source=recommendations
However, you can reach Azure support on the global service numbers: https://support.microsoft.com/en-us/topic/customer-service-phone-numbers-c0389ade-5640-e588-8b0e-28de8afeb3f2
or https://azure.microsoft.com/en-us/support/create-ticket
You can mark it 'Accept Answer' and 'Upvote' if this helped you
Regards,
Abiola