You are truly novice in torture. Best way to torture someone is not through ending his life - tempting it might sound - it's rather preferred to lead him to wish such ending. Now that whipping is not getting through him as it used to be once with his body starting to endure it less effectively, our next step shall be of a better effect. First thing we're going to do is chaining him to a steel chair, put his feet in cold water, and light a small fire under the chair. Then we're going to struck few nails through his fingers, preferred small nails since we don't want any permanent damage; cutting his fingers. We could also spice it up, and surgically inserting a few insects into his heart just for the chill of it. Later on, we're going to take it to the next level; bringing a hot bowl of oil and some sponges, and rub it on his chest, which reminds me, we could also put a picture of Justin Beiber in front of him which blocks his entire vision for that picture to become the only thing he's able to see. I have allot more in mind, but this is just day 1.