Mail Blocked

Hi, I have been recieving email since Friday 5th June, about exceeding outgoing email quota therefore being blocked as a result. I have unblocked my email several times since then, and the message keeps coming back with:

We regret to inform you that your email outgoing has been blocked and you will not be able to send further emails.This was done in accordance with the Zoho Mail Usage policy.

Reason for the block : Daily Mail Size Quota Exceeds Limit [Total Mail Size=307,200]

Is the total mail size in KB? Is one of the problems this may be caused by is by having the account open on various devices therefore it thinks that I am sending multiple emails?

Sorry don't understand how this works... Please explain, why this is happening and how i can fix this asap!

Thank you