heating/ thermostat

What is your question?

My check engine light came on did the electronic test and it said coolant temp low. so i asked a few different people and they said the thermostat is stuck in the open position so i bought a replacement thermostat and changed the two out. i reconnected the hoses and bolts/ refilled the coolant anti-freeze had the engine running to ensure that their were no bubbles running through the hoses and all seemed well. had the car running for about 15 minutes or more. went to check the heater inside the car and the air was ice cold. the previous thermostat would at least heat up my car after awhile but this one isn't doing anything. is their a valve i need to open or that i missed any help would be greatly appreciated. 2004 mazda 3 sport sport shift automatic 2.3l 4cyl