Are you filling up the overflow tank or the top of the radiator?
The overflow tank is just for that, overflow, the top of the radiator is where the fluid would need to go.
If you are filling the radiator and not the overflow tank, and you correctly replaced the thermostat then it is most likely a water pump issue; not sure if that car has a serpintine belt (1 big belt for everything) or individual belts for ac/water pump/ power steerin/alternator but check and make sure that the belt is there and is tight, otherwise it is an issue with the pump and you will have to replace it. The pump itself is not expensive but it requires a moderate amount of dissassemly to get to it, due to the time required to get to the pump it is always highly advised to change timing belt/pulleys while in there vs paying all the labor to dissasemble the same area.