Acrobat X Pro no longer works and does not recognise the purchased serial number from 2013

Acrobat X Pro no longer works and does not recognise the purchased serial number from 2013. Any advice based on actual experience of a successful fix will be most welcome.

Something that Adobe has altered causes our purchased, registered and perfectly valid Acrobat X Pro (part of CS6) to cease functioning after 7 years. The other CS6 programs are functional but something is causing Acrobat Pro not to recognise the serial number any more, and not only demand that we "continue a trial" of 32,727 days - that we never signed up for, but after the second fruitless attempt by an Adobe technician to fix it by remote access to my desktop, they have put the problem they have caused* into the too-hard basket, referring it to this forum.  (Hardly away to endear one's firm and keep loyal customers, by the way!)  

Since Adobe's last remote access attempt to fix this, Acrobat no longer stably opens a document - clicking "continue trial" just blitzes the program, so nothing is possible.

Two extended attempts at fixing the problem by remote access have failed, and a new serial number was promised just for Acrobat Pro - but this morning one of their chat staff claims that Adobe cannot fulfil that promise made to provide a working serial number - and makes no attempt to provide an actual solution, but fobs the problem off to this forum.

After the Adobe message promising the new serial number was sent, there was a subsequent email from them telling me to use legacy files 1 and and 2 for CS6 (links provided) and do a complete uninstall and reinstall, but that's EXACTLY what Adobe did remotely on my desktop, and it not only did not work, but made things worse.   Now, after that intervention, I can’t hit the “Continue Trial” buttton without zapping the document and crashing the program.

I’m desperate to get this fixed – it’s only nine days until the Rotary Youth Driver Awareness Day that I am organising, and I cannot even open the pdf questionnaire returned by the crash survivor, much less modify it as I need to do. Over 200 people and two schools depending on me.

* it seems to me from the sequence of events, that the problem is a consequence of an Adobe update linked to their attempt to squeeze everyone (including charity organisations) into a subscription arrangement to use their software.  If I'm right, this piece of technical trickery is counter to what in Australia is considered a legal contract attendant on our Rotary Club's outright purchase of the CS6.