Cloud programs do not use a serial number... you log in to your paid Cloud account and whatever plan you bought is available
Link for Download & Install & Setup & Activation problems may help
Welcome to the Adobe Forums,
Adobe CC does not require serial number, to install & activate it, please go to www.creative.adobe.com .Download, install & activate it from there.
Please let me know if it is asking for serial number when you are trying to activate the CC.
In that case, you can follow http://helpx.adobe.com/creative-cloud/kb/ccm-prompt-serial-number.html.