Lost serial number for original product, upgrade is now unusable
I originally purchased CS3, then upgraded to CS4 in 2010 (purchased direct from Adobe). Three years ago I started using Creative Cloud, but I can no longer justify the monthly fee. So I re-downloaded CS4 from My Products, entered the serial number as requested, and ... was asked to enter the serial number form CS3. Which I no longer have. According to Adobe, my only option is to buy the software again. Is there any way around this?.