2002 VW Jetta running hot

I have a 2002 Volkswagon Jetta it was trying to run hot but never did. We had a freeze last week and my heater stopped blowin hot air just cold air. And it seem like it was trying to run hot even more. I received severally different opinons from different mechanics. They said it could either be my thermostate, the heating cord, and they all said I had a leak. So I brung it to a mechanic that said he knows how to fix it. He changed the thermostate and changed the part that was leaking(water outlet). But now my car is actually running hot. So he changed the thermostate again due to the first one he used was not a high performing thermostate. But my car is still running hot. He then said that he didnot know what the problem could be. He said it might be the water pump but he is not sure. I told him that another mechanic said it might be the heater cord. But he said he was sure that it wasnt the heater cord. But my heater only blow hot air when the car is running hot. I dont know what else to do, I have brung my car home and dont know what else to do.