What did you purchase and how much did it cost?
We apologies for the inconvenience caused to you. You can purchase Lightroom in two ways.
1. Lightroom is available via Creative Cloud, wherein you don't require a serial number to activate it, you just need to sign on the Creative cloud desktop app.
2. Lightroom is also available as standalone version and for that you need a serial number to activate the software, If you have purchased a standalone version then you can find the serial on your adobe account. refer: Find your Adobe product serial number quickly
I have checked your account and I see that you own the standalone version of Lightroom and serial is sent to your email address.
I purchased same product with disc to install
says I don't need serial number, but when trying to install from disc a Numeric only serial number is needed.