This alert should soon be automatically cleared. If you have removed these roles you have no further action.
You can also ensure that there are no remaining classic administrators in the system by going to Subscriptions > Access control (IAM) and ensuring no users have the classic admin roles .
However if you want dedicated support you can create a support request for the support team to look into your account: https://azure.microsoft.com/en-us/support/create-ticket
You can mark it 'Accept Answer' and 'Upvote' if this helped you
Regards,
Abiola