Did same few years ago, ported from Reliance CDMA(pre-paid) to Vodafone GSM(pre-paid),
my number was ported in close to 7 days, didn't had to go reliance, just went to vodafone store
they asked for port code (SMS) and gave me new Voda sim & told to check reliance SIM, if there's no network that means your number has been ported. at zero cost