There are several different thing.
1. Check your engine temp, if you have a temp gauge on the dash. Look to see if it is in the normal range. If the engine thermostat is open, the engine will not get warm and you will not have heat. Replacing the thermostat is not expensive.
2. If the engine is operating at normal temp, then the controls for heat and cold are not working. This could be more expensive.
3. The heater core could be plugged up, but your car is not that old.