Cs6 Design and Web Premium

I'm trying to figure out how to download:  Cs6 Design and Web Premium.  We previously purchased this product on CD disk in 2013.  The disk was purchased for Academic use and had 4 licenses.  The original CD has been lost and I'd like to download a single copy of software to a new computer (Dell Optiplex 780, 64-bit, Windows 7; 4Gb RAM).  I retained the SN from the original installation disk.  But under my Adobe account, the SN is not recognized as valid and I also cannot register the SN as an old product.  Plaese help.  Not sure if: 1) purchasing through our academic vendor 2) purchasing on a CD originally or 3) creative cloud or whether other download portals are at issue here?  Need some direction?

Thanks,

Paul

UMass Medical