You have oil backing up in your coolant reservoir and you have no heat in your car what do you do nowwe cant find the thermostat.we replaced the radiator and that was no help what do i do now?

Oil can't "back-up" into the coolant, they run in separate systems... you wasted money on the radiator, the thermostat is irrellivent, your engine block is probably cracked although it could be a gasket or loose bolts... you need a good mechanic and money