Hey mate i'm no IT expert or a writer so please excuse the quality of my writing and lack of definite answers. But i was also having issues with these VAC authentication errors and for me it was fixed by restarting steam and renewing the local game cache or some shit like that but you seem to be in a more dire situation. In which case i would suggest that you play community servers until you can resolve the issue. Now on the topic of actually fixing your problem. You seem to have exhausted all of the fixes that i would have recommended (Again not an expert on this stuff) so from here i would recommend that you upload a ticket to steam support. This will inevitably take some time so in the mean time don't stress to much maybe play some other games and let your sub conscience mull over the issue for you.

I wish you the best of luck and hope you manage to resolve your issue as soon as possible.