Help! I'm locked out of email because full. But it's not! Support gives error messages

Help, I am locked out of my main email (hotmail) account.   If I try to send email I get:

This message can't be sent because your mailbox is full.

But I have purchased basic 365 and when it checks it says I'm only using 24% storage.

When I try to contact customer support via web chat I get an error message.  I've rebooted twice, still stuck.

Any help greatly appreciated!