If you paid, then you have avast! Pro. The other product is avast! FREE for Home use only. If you paid, then you were sent an email license or cade. The file is “license.avastlic”
Either you paid for Avast Pro, or for AIS. When you paid, you probably provided an email address. The same email address should had received an email. Check you “junk” email folder.
If you still don’t find it, look at http://www.avast.com/license-center so to receive the email again (but the email address you will provide now neeeds to be the same one you used the first time).
I always liked to hide a copy of the “license.avastlic” in the root of drive C:. Nobody ever looks there, so it always persists no matter what users delete.