possibility one: plugged heater core or stuck thermostat. not likely with that low miles, but possible. see if both the lines going through the fire wall get hot.
Possibility two: heater mixing door is not working for one reason or another. This is the most likely problem, but not as easy to check. I am not sure where the mechanism is located on your car, but if you look under/behind the glove box it is probably there somewhere (may involve sitting upside down in the passenger seat.) Not sure what you can see, but you may be able to see a rod that is supposed to turn to open the control door. with the heat on, adjust the temperature, and you should be able to see the rod turn. if it doesn't turn, see if you can turn it by hand to adjust the temperature. If you can turn it by hand, there is probably an electrical problem, either with the temperature selector, or with the mixer control. If it doesn't turn by hand, suspect some kind of mechanical problem with the mixer.
Just to give you an idea where to start looking. This is not exhaustive, just from experience with my grandfathers Buick.