Inbox deleted IOS/icloud

Hi there, I have a me.com email address that I use on my iPhone 7+ (11.1.1)/ipad/imac. This morning (18th) I was checking email using the mail app on my iPhone and I saw a whole bunch of emails being deleted as I was reading. I now have nothing in my inbox or bin before the 12th December. My sent items still has everything back beyond that date.

I have checked my iPad/Imac and logged onto my icloud account on my browsers and I have no messages before the 12th in any of those. I have checked all of the other folders in case I inadvertently moved them but nothing is contained in any of them.

Does anyone know what I have done, or more importantly how to retrieve these emails. I would have thought if I had somehow deleted them then they would be in my bin so I am hoping that given they aren't there that they have just been moved somewhere.

Thanks for any advice