Having problems when entering serial number

Hi,

we're having a Creative Cloud subscription for enterprise and we received the serial numbers. Because the user already wanted to test the software, they installed the trial version, which ended. Now, we're trying to activate the software by entering the serial number but we get this message:

Serial Number xxxxxxxxxxxxxxxxxxxxxxxx you provided is not valid for subscription products. To use this serial number you need to follow these steps to download and install perpetual copy of this product: ...

I already tried to uninstall the cloud software and reinstalling a trial version and the inserting the serial number when launching but we always get this error message. How can we solve this?

Kristien