You need to find a propane dealer that has a pressure gauge to test for pressure. I have a hard time believing that the line could be plugged in the middle. The quick connector could be plugged though at the point where you plug the grill in.
Are you sure that something in the grill itself is not plugged. I know that you said that you checked but, that would be the easiest thing to fix. There has to be a valve on the grill to control flame height. Are you sure the knob on the valve is turning the shaft that it is connected to ??? Could there be a chunk of dirt that fell into the grill line and got stuck at the valve ???
Hope you get it fixed easily. Have a nice day