Add toner light will not go off

pull apart the toner bottle holder and check for the 4 little lylar paddles inside. if they are not attached, one of them may have plugged up the entrance to dev unit. vac out all inside and reattach the mylar paddles or order new ones if necessary

There are several possibilities, they can be damaged the add toner motor, can be damaged the roller paddle in the UR, It can be obstructed the fall of the toner holder, or broken the latch that releases the fall of toner. Or simply the mechanism that opens the bottle is not working well.

What "t" I'm not sure what you mean...where? any other lights on other than "add toner"
As for the toner...Was the 'plunger' in the top of the bottle you removed, or did it possibly get stuck in the machine? If the old plunger is still in the machine it will block the flow obviously. Remove the new bottle and check to see.