Recently I have bee trying to set up an underground town, but whatever I do I cant seem to get the npcs in question (clothier and demolitionist) to sell the pylon. I off Started of putting them near the end of my hellevator (small world), then I thought maybe they were too close to hell, so I moved the town up about 250 blocks. After this failed, I though maybe it is too close to the center of the world as my surface town is right in the center of the world, so I moved the town about 600 blocks east. This didn't work either. Then my final attempt so far came when I realized that they are still quite close to hell, so I moved them to the midway point in my hellevator and about 100 blocks east. Still hasn't worked. I should have attached some screenshots of the few towns I have built. Please let me know what I have done wrong if you know.
(i have put the images in chronological order)