WordNet sense 1 (stubbornly persistent in wrongdoing):

obstinate, unrepentant, cussed

WordNet sense 2 (not reformed morally or spiritually):

unregenerate, unregenerated

WordNet sense 3 (showing unfeeling resistance to tender feelings):

flinty, granitic, stony

WordNet sense 4 (lacking in feeling or pity or warmth):

heartless