That's weird @Maureend
Are you using the stock email Samsung app ?
Depending on the type of email account i.e pop3 or imap I'm wondering if your own email server is somehow sending them back to your phone's email app when it syncs.
Perhaps go into your email account via logging in through your url bar or another device and delete them this way and then see if they appear back in your phone's email app.
I wish you all the best with this
Current Phone ~
Samsung Note 20 Ultra 5G SM-N9860_256Gb SnapDragon 865+
Samsung One Ui 3.1/ Android 11.