That link only suggests contacting Microsoft. Which is something you possibly need to do. There maybe an issue with software selling vendors and their bulk procurement for resale versus valid keys.
Also of an off topic note, when I searched for a copy of Autodesk, I saw some places selling the suite I needed for OVER HALF the retail cost. I was IMMEDIATELY wary of those places, as they may have certain "workarounds" that may not work and go through their "activation" centralization - meaning the vendor (not you solely) having license control.