I thought I had sorted my problems by upgrading to 13.2. It was short lived. I then did as you say and deleted my iPhone and iPad from devices in exchange admin online. I then deleted the accounts of both the iPhone and iPad. Rebooted the devices. Re-added the accounts. Immediately, the same problems returned. But worse. I have to delete emails twice again, but this time they are not in any specific order. I delete one, and the next email appears, exciting me as I think it actually deleted, only to find that after deleting a few more emails, the ones I deleted 5 or 6 emails previously suddenly need deleting again.
This is not an active sync bug. Apple have broken their mail app and are not making it compatible with active sync as they should.
Apple have not been helpful with me regarding this at all. Expecting me to do full restores on my devices etc. Not going to happen. Just fix the bug. It wasn't there in iOS 12, it is in iOS 13. They broke it. They need to fix it. People will go elsewhere. Apple used to have unofficial slogan "it just works". No longer the case.