There have been similar reports on the forum and one of the common things is that all the users used iPhones or iPads to access their email and when BT checked to see which device triggered the deletion it was either their iPhone or iPad.
If you have checked and the emails are not on the BT servers when you use webmail it means that they are gone and can not be recovered by BT.
Not much use now but in future do not use the email inbox as a storage folder. If you have emails that you want to keep you should set up a new folder and store them there or better still download the emails to your PC and store them in a folder there. You could easily do this by setting up an email client on your PC and set it as a POP3 account instead of an IMAP account which you would appear to be using now on your Apple devices.
You should also include the email folders in your backup regime, assuming you have one.
It is possible that your phone had been hacked but obviously it is not possible to say for certain that is what happened or indeed if it ever happened.
Normally when an email account is hacked the hackers usually harvest the hacked accounts contacts and at some point send phishing emails purporting to be from the hacked account holder to the contacts in an attempt to get something from them or get them to click a link or download malware onto their device so it may be worth informing your contacts to be aware of any such type of email purporting to be from you.
