Reinstall Adobe Acrobat 9 - tells me invalid serial number.

Before reloading my machine, the deactivate was greyed out from Adobe Acrobat 9. Customer service told me simply to reinstall after reloading my machine and activating the new install. After downloading the link to the Adobe 9 Standard install, installing it, and putting in my VALID serial number, it tells me INVALID SERIAL #. My Adobe account says it's valid. I do not have hte original CD or download. I don't know what to do at this point - help anyone??? I have Windows 10 for OS.