Impossible to send mail for 500 5.4.6 - What is the limit? can you restore our account?

Impossible to send mail for 500 5.4.6 - What is the limit? can you restore our account?

Hi,
We are sending one email every twenty seconds for GDPR.
After sending 400 mails, we cannot now send any mails for an error 
Impossibile inviare il messaggio;Motivo:550 5.4.6 Unusual sending activity detected. Please try after sometime

This happens both from an SMTP client and from the web client.
Can you restore our ability to send mails and explain how many mails we can send?
This is a paid service for us, we find it very weird we cannot send new mails or know what our limits are.
Thanks
BVEvents