The newer propane tanks have a valve that automatically stop the flow if the tank is over filled. If your tank has a triangular shaped handle on the valve it is equipped with an Overfill Protection Device (OPD) valve.
As the tank is filled this OPD will keep the gas from entering the tank once it is 80% full. Maybe this valve is stuck closed.
Or
Once you hook the tank back up it can take a long time (up to 5 minutes) for the gas to get to the appliances. I use one of the burners on the stove, turn it on and every 10 seconds try to light the burner with a BBQ lighter. Keep windows and door open for ventlation.