ADOBE ACROBAT 9 PRO EXTENDED SERIAL NUMBER DID NOT WORK

I purchased an ADOBE ACROBAT 9 PRO EXTENEDE a few years ago. It was crashed in my old computer therefore I uninstalled it and wish to reinstall it and found out the serial number was invalid.

I purchased it and kept it with me all the times, how could it invalid.

I called the customer service. They gave me a adobe acrobat 9 pro link which did not accept my PRO EXTEND serial number and move me to the forum. Do we have any expert here that could advise?

Thanks

Lucy