network unlock for free

how can i network unlock my samsung galaxy light for free i am just 17 years old i get no credit card please help me i want to use my phone to make calls and text and surf the internet and cant because of when i put in a non provider simcard it ask for network unlock code................please i need help:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:( :(:(:(:(:(