Messages Hacked

My Facebook messages are being read by someone other than the intended recipients. The little check mark at the bottom and the text "Seen at.." is showing up on all my messages fairly shortly after I send them, and they are NOT being read by my friends first. I have confirmed this with them. My messages are being read in the late evening when most of my friends are no longer online. And this is happening with ALL my messages, not just with certain friends.

This is not a typical Facebook hack. if someone was simply logging onto my account to read my messages, the checkmark and "Seen at..." text would not be showing up at the bottom of the messages.
This is something else entirely. Someone has access to every message I send to EVERY friend on my account as if the hacker is the RECIPIENT of ALL the messages.
This means the security and privacy of my account and that of ALL my friends has been severely compromised - YET FACEBOOK HAS NO CRITERIA FOR REPORTING THIS!!
I have APPLIED and RE-APPLIED all the privacy and security tools, to no avail.

I tried contacting Facebook via the most relevant and similar criteria I could find - only to receive a message - from an actual person - that the issue would not be pursued because I was using the improper criteria or forum.

Unbelievable.

Catch 22, here we go round the rosie -
Apparently there is NO WAY to inform Facebook that their message security is sh*te, that their system is apparently WIDE OPEN, and it appears they don't really seem to be all that concerned.
So my only recourse seems to be to either deactivate my account, which I shouldn't HAVE to do - Facebook should be able to investigate and resolve these issues since they are quite serious - or I can get the message out and try to make it go viral that everyone's message privacy is severely compromised - uhhh, I mean, NONEXISTENT.
Thank you for your forum and whatever advice you may have.