email – complete iPad mailbox

I have a web mail account that runs primarily on an iPad mini. This seems to be constantly full despite the emptying of the inboxes and mailboxes sent and the severe pruning of the inbox. Currently, I can not delete the mail for any reason, a pop-up window saying "can not go to trash". When I go directly to the webmail via a server, I can dump about 2% but that's it. I've accidentally had a list that displays 585 messages, suggesting that they're archived somewhere, but they disappeared before I could do anything. I do not have any archived files that seems very strange and despite the following suggestions listed can not find anything. I do not use iCloud addresses or Gmail addresses. HELP ME.