Activation Code for Razer Kraken obscured

I received a Razor Kraken headset as a gift, so I don't know the purchase date or have a receipt.  When I scratched off the activation code, the first part of the code was mostly scratched off.  I only have about the last 15 characters, so I can't activate the 7.1 Surround Sound software. How can I get an activation code?  I do have the serial number.