What am i meant to do now?

I am a 38year old guy and i have a 15 year old son who goes to a secondary school. My son is a popular boy in school and most of the boys and girls all like him. He seems to make friends easily. But i always thought that my son would never bully anyone and i found out last week that my son has been bullying a boy who is in the same year as him, but my son has loads of friends where as this other boy doesn't have many friends and he has been annoying this other boy for 4 months now. I have always told my son never to bully anybodyelse and i thought he new right from wrong as he has never been not nice to me, he always seems to show me respect. My son kicked and punched the boy and my sons friends helped him. I hate bullies. I have said to my son that he cant do that but he doesn't seem to be listening. He just lives with me as his mum is dead (she died when he was 6). I have told him to stop annoying the other boy but he has been continuely annoying him over the last couple of days, i know this as the boys father came to see me as he was the one who found out what has been going on. My son uses the other boy as a punch bag as he is a quiet and shy boy and i have told my son to stop annoying him. The other boys dad came to see me yesterday and said that he wants me to stop my sons behaviour, the school have got cctv footage of my son attacking the boy, and the man has told me he wanted me to use a belt on my son infront of him and his son to teach him a lesson. I said that i dont feel comfortable doing that, he said he would go to the Police otherwise and show them the cctv as it is up to him if he wants to press charges. This could ruin my sons chances of getting a job. So i said yes to the guy that i would my son infront of him and his son using a leather belt. He came over today at 6pm to my flat with his son. I had told my son what i was going to do to him infront of the two of them. My son didnt even know that i was going to use a belt on him, i have never done so before. The other boys father said to me he wants me to belt him at least 60 times with the leather of my belt. I said to him are you crazy but he said he wants this to stop once and for all. I then called my son out of his room and he was suprised to see his victim in the iving room but i said to him you have to be punished for bullying this boy and you are going to bend over the side of the couch and i will you. He said to me you are joking right?, But i told him no. He then started to run away but i grabbed him and i pushed his head inbetween my legs and i ripped his trousers and boxers down. His bare backside was facing the boy and his father and i belt my son nearly 70 times. My son was screaming for me to stop but i never did. The other father started saying do i hear you say sorry, my son started screaming sorry about a thousand times. The other boy and his dad started laughing and by the time i had finished my sons backside was red raw, some of the skin had even peeled off. My son is still really upset as the victim took a video and he is threatening to show it to my sons friends in school. After i had finished him i let my son out from between my legs and i had himby the back of his jumper naked infront of the man and his son and he said he was sorry and he was crying with real tears. The other boys face was balck and blue from what my son had done to him but he started smiling as if he was enjoying seeing him go through. I feel as if my son has really being punished but i dont know if i have done the right thing. My son has gone in a huff and he was saying that the other boy who he bullied will have shown his friends the video of him getting ed. Did i do the right thing??? If i hadnt ed him the other father would have pressed charges. What should i do now? Has my son learned his lesson or will he continue bullying someone else??? Was i in the wrong to him???