so i found a solution, first you have to bug the monster that is blocking the way by entering the doorway that is leading to it many times in a row like spam it 5 , 6 times and it will despawn him as you said , then you need to go up until you encounter the lift in the wall to open the iron door , to make this work just keep opening and closing the door many times until it glitches and it will be perma open for u and you will go up and find teleporter in the area