As you found, the online and CD products are priced differently, and buying a CD does not give you access to an online download. You also can't associate your CD copy with more than one owner. (The license allows you to install your copy on up to 5 computers that you own, it does not allow you to install your copy on computers owned by 4 of your friends or family members.)
There is a 60 day refund policy on the CD, submit your request here. (They will verify, for example, that you bought your CD from an authorized retailer.)
https://ttlc.intuit.com/turbotax-support/en-us/help-article/intuit-account-billing/turbotax-satisfac...
If your son purchases a new download from Turbotax, or from an authorized reseller like Amazon, it will come with a new installer code and should be able to be installed and associated with his online account.
