I would try grating some into his food. If he it's his food with it on it, then, maybe do bigger chunks next time, then see if he will eat from the block.
Mine won't touch it either. Try some cuttle bone instead. If they are getting a good diet and some occasional calcium powder, they often won't touch any other supplemental calcium sources.
I have a cuttle bone as well and can tell it is nibbled on occasionally. I also do powder 2-3 times a week lightly sprinkled..Ill try shaving some off into food..Thanks..