Can you post the model number of the appliance please?
The most likely cause of this problem is the front thermostat is open circuit.
You need to test this with a multimeter to see if it's open circuit.
If it's ok, and if the wiring tests ok, (you've already replaced the heater and thermostats at the rear) then it only leaves the drying module as the possible cause.
Check the front thermostat, let me know what you find and get back to me if you need more help.
Hope this helps
what does the front thermostat look like and where is it located
It's a circular shaped item and its fitted to the front housing that the drum runs in.
Take the top off and have a look, see if you can see the terminals sticking through the housing.
The wiring diagram shows a double black/white wire on one side of it and a black/white wire on the other side of it.