Why is my ex-husband so condescending? Especially when it comes to our kids!?

background: been apart for 6 yrs/divorced for 5yrs. He pays 1/2 of what he is court ordered to pay in child support, doesnt provide insurance, school supplies clothes etc.. He does get them almost every other weekend & a few weeks in the summer. Here's the current issue: my son (14) has that shaggy haircut, earlier in the year he got into trouble at school & i took his cellphone for a month & told him he had to pull his grades/behavior up or lose the phone & the hair.School is out they are at their dad's and my son just texted me frantic "my dad's going to make me cut my hair!" So I call his dad & POLITELY ask whats up with the haircut? we getting a trim or what. He goes back to the deal at school & I explain that he straightened up got his grades up etc.. So now he gets pissy & condescending about the haircut saying " Whatever YOU want YOU make the rules its however YOU want it. Am I wrong for feeling that my son & I should be in on that decision? Y must he be like that