First scan your email devices for unexpected virus, trojan or other malware that may be capturing your passwords. Change your TalkTalk mailbox password to lock out any email app or mail collection service that's downloading and deleting your mail messages older than 1 week. Upgrade the password and make it unique to the email address.
The Reset password now button in the help article Changing your email password will take you to password reset and recovery.
If you have set up password recovery options, in advance, that you recognise from the *****hints, then you can send your alternate email address a link or your mobile a 6-digit code to authorise a password reset.
Have you recently set up a new email account on the Mac or the 'phone? If so, my diagnosis is that the email account has been set up as a POP3 account that will download from the Inbox and then delete, in this case, messages older than 1 week. That's a setting on the POP3 email account. To keep mail messages for longer on the server then the setting must be 'never delete from the server'.
If you haven't set up a new mail account then it's likely that your mailbox password has been compromised. Hence the up front advice to scan for password capturing malware and to upgrade the password.
TalkTalk Mail does not delete or archive mail from the Inbox after a week so email software that's doing this is external to the mailbox.
