OP, I don't want you think that we are X-bashing. My brother was an incredible divorced dad. That's one of the reasons I feel I can safely say that you were right not to pay. It was your STBXH job to cover himself and his child.
There are great fathers in the world, and horrible fathers. Same is true of mothers. In the case the OP is in the clear and her STBX is a jerk.
My BIL's X used to love to tell their daughter she couldn't do X, Y, Z because Dad wouldn't pay. For the record the only thing he refused to pay for was a subpar private school, when the public school she was zoned for was far superior.
It backfired on the X. When niece was old enough - they showed her records of the payments they had made that for activities she never got to do because her mom drank/gambled the money away. (Happened because she yelled at them about getting braces - Mom had told her it was their fault she wasn't getting them. They showed her the account they had set up with the ortho money in it.) Niece played a wicked stepmother in a play - said she had the perfect real life model - he Mom.