I am really mad at my friend?

My cousins and I prank phoned call one of my guy friends as a joke, since he likes prank phone calls I figured he get a laugh from it. But then to get back at us, he put her number on the personals section of craigslist and my cousin got nonstop phone calls from guys. I called him to tell him to put it down but he denied ever doing it. I know it is him because it sounds like something he would do. A month later (today) he put up her number again on craigslist, again I asked him about it and he denied it and acted like he knew nothing. I got so angry I yelled at him and said some very mean things. I just am so mad that he is acting so immature and I hate the fact that he is messing with my family. It started off as a joke but he is taking it way too far and the fact that he refuses to admit he did it makes me even more angry. He texted me wanting to know what I did wrong but I just don't know what to say since he won't admit it. What should I do?