Most emails have disapeared and seem unrecoverable

Hi Guys,

I access my emails via my ipad and iphone on a daily basis and on the occasions via the web interface.  I have found of late that all my emails from before the 5th September have gone from my account and there was some very important emails that have now gone and will cause me some issues if they are not restored to the account.  I can not see any setting within the account that will auto purge any emails and the account is actively accessed so it should not fall into your policy of purging an inactive account.  I have also tried the restore deleted emails but this only worked for the deleted items folder not my inbox or sent items.  This sort of thing does not happen with other providers.

Please advice as soon as possible.

Thanks