CS6 Master Collection fradulent license number

I purchased CS6 Master Collection disc on eBay in December 2017. It was probably the last CS6 Collection sold, as far as I know. I had to buy CS6, because (as many of other freelance designers) I can’t afford to pay every year the same money with what I can purchase a complete set of programs for good. Before the purchase I was provided with additional photos of the box and the license number for checking if it’s legit. I registered the license number on my Adobe Profile as a product.

It went through the verification and it registered as CS6 Master Collection, now bound to my profile, so I thought everything went well and there was no doubt that I could proceed with payment without fear. The seller, with whom I was in contact with for more than a week – asking about everything that I deemed important and to make sure everything was legit, thanked me for my purchase and gave positive review. The disc came by mail after about a month.

This month I have been finally able to install it. The installation went perfectly, I put in the license number, it verified and was flagged as OK, and I installed the software. Did some work on it for the rest of the day.

The very next day I opened the programs it now wanted me to put the license number in again. Weird, I thought, but put it in anyway. Suddenly, the number was revoked. After contacting Adobe Support, I was informed that the license was fradulent and there was nothing I could do to use the programs. They told me that even when I verified and registered the product od Adobe Profile, installed it with the license number (which was again verified by Adobe) and used it for a day without problems, I couldn’t really make sure if it was legit or not. I was of course also advised to upgrade to CC (how original).

Is it really true that Adobe can’t verify the license, even if they had it registered on my profile for more than two years (never sent a warning, nothing), flagged it as OK during the installation, but SUDDENLY a day AFTER installation it is revealed as fradulent?