Can not activate After Effects CC

I have been previously using After Effects trial version and after it expired I bought an annual plan for it. When I try to launch the app it asks me for the serial number, which I don't have. I understood that it should automatically activate the app but that didn't happen. I tried reinstalling After Effects and Creative Cloud, but that did bot help. Can you please help me through this problem, how do I activate it? I would be very thankful.