my me.com is not receiving emails and says 'over quota' to the sender

My me.com email is not receiving any emails and people sending me an email have a reply from apple saying 'over quota'. I went into an Apple Store just now and they didn't know why it's doing this, and said to delete emails from my inbox. (about 4200 in my inbox and 8000 archived) because it's probably reached its capacity. I have over 10gb's of space on my iCloud account and only 11.3mb of it are being used for my emails. I have started to delete emails. Several hundred, but after sending an email to myself from another account, it's still saying 'over quota' in the post master response.

Has anyone else had this problem, and if so, how was it fixed? Quite frustrating as it's my primary email address and am missing out on important emails.

Thank you!