Moving Photoshop Elements to a new laptop

This always seems to be a problem. I purchased Photoshop Elements 15.0 a few years ago and have been very happy with it. I have just purchased a new laptop and moving /installing my programs onto it. I have downloaded Photoshop Elements 15.0 but when I enter the correct 24-digit serial number dialog says this is invalid. On troubleshooting page I have tried some of the solutions (solution 1 said use the correct installer but I have NO IDEA what that is!; solution 2 said delete activation base files but the particular ones are not on my computer!; solution 3 run the CC cleaner tool which I did; solution 4 says run in trial mode then convert but I can't download elements15 in trial mode; solution 5 create a new account - I've done this and tried to reinstal but it still rejects my 24-digit serial number. I have tried logging into my adobe account to check the correct serial number is on record and it does not show my elements software at all!)

Soooo. Very frustrated over trying to do what everyone must do when they upgrade computers!