Change the password from a trusted device, revoke sessions, enable/repair MFA, review forwarding/rules, check for suspicious sent mail and contact DAIM HUB if the account is business-critical or wider compromise is suspected.
For security, payment, legal or business-critical issues, stop if you are unsure and contact DAIM HUB through an official channel before making irreversible changes or sending sensitive information.
What to do next
If this answer does not fully match your situation, do not guess on a production, security, payment or data-related change. Contact DAIM HUB with the affected service, what happened, when it started, business impact and any safe screenshots or error messages.
Help Centre content is general guidance. Your final signed project Scope of Work and agreed terms and conditions take priority where they differ from a Help Centre answer.