I cannot get the Evolution trash folder to empty

Hi. I have tried File - Empty Trash, and also Folder - Expunge. Neither works, and I am now getting to the stage where messages are taking up way too much space. I have 8304 deleted messages in the trash, and do not seem able to get rid of them. Any suggestions? And by the way, I don't have a great knowledge of computer commands etc, so you will need to spell it out for me lol :)

Thanks, Andrea