Deleted emails keep coming back in Mail app (on all Apple devices)

I have an iCloud email address (@me.com) and all my old deleted emails keep re-appearing in my Inbox and the emails keep on piling up every day, it's driving me insane! It is a huge inconvenience when trying to find save emails.

I've looked up solutions and tried several, and none of them work so far. I did a hard reset of my iPhone, I signed out of my iCloud account and signed back in, I changed the settings for the Mail app, I deleted the Mail app and re-installed it on my phone, nothing works!