email

You can go to https://getsupport.apple.com and work through the options to find the section which covers your problem. You will then be offered means to proceed, and this may include online chat or ring-back to your phone.

In the USA you can ring (800) APL–CARE(800–275–2273). In the UK 0800 107 6285

For other countries go to the main Apple page for your country and click the 'Contact Apple' link near bottom right.

It may be a setting on the email server. If it is a corporate Microsoft Exchange account a lot of businesses automatically remove email periodically. It can also be a setting on the phone; go to Settings/Mail/Accounts, tap on the account and check the setting for Mail Days To Sync.