There are multiple channels for doing so depending on your requirements. I work for an organization that has many Microsoft services and I am not aware of an Account Manager/Representative. We use the support accordingly for any questions:
Azure support ticket
https://azure.microsoft.com/en-ca/support/create-ticket/
Admin Portal for 365 Support
Contact Microsoft Azure Sales
https://azure.microsoft.com/en-us/contact/#contact-sales
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