My 14 yo son defied me. I need advice

My (only child) son is a teenager. I try to take his teenage angst, rebellion and grunting in stride.Saturday he helped me in the yard for about 45 minutes. I told him that I appreciated his help, and was going to need about an hour of his time on Sunday to help me with the garage. I even offered to take him to his favorite place on Sunday for lunch, as a "thank you" from me for all of his help.When I went to his room today, and told him it was time to help, he told me "no". I explained that I had given him fair warning about the time that I would need him, and I expected his assistance. And if he didn't help me, I was taking away his computer for 24 hours, and I would not be "helping him" this week by picking him up from his (passion in life) sports practice....and that he would need to find someone else to bring him home.He looked at me and flat out said no. When I tried to take his computer, he body blocked me. I then left his room....and when he went to that bathroom, I went in and took his computer screen.He later came to me and apologized for not helping...."but"....he was feeling overwhelmed with all of the work he was helping me with (45 min on Sat) and how he had no "downtime" (despite the 23 hours on Saturday he spent in his room).I explained that a true apology included: I am sorry that I did this, It wont happen again.*And this is what I am going to do to fix this.I then suggested that he go to bed and we can talk about this in the morning.Bottom line: I am feeling unappreciated and disrespected.How would you handle this? via /r/Parenting http://ift.tt/2wNi3ms