What do you do if your kids' dad plays "Santa Clause" with the kids and leaves you to be the bad guy?

I have two teenaged girls,I am divorced from their dad and have a new husband of two years now.My kids' dad gives them money all the time and they are very good with him(of course).I am left to do all of the disciplining and left to see their bad side and smart mouth,etc.I call him and ask him to talk with them about it and he won't.He says it's my problem cuz I left him and took them with me.They are not little,they are 15 and 17.It just sucks that he's just the "money giver" and I'm the "warden".My husband,the kids' stepdad,tries to help me but if he so much as blinks the wrong way,they tell their dad and he starts trouble.It's a messed up situation.I end up with a couple of spoiled brats that don't listen cuz daddy gives them money and they like him better I guess.I do alot for them too.It's just messed up the way they talk to me.Any suggestions on how I can not be seen as the bad guy just cuz I'm the custodial parent?The girls' stepdad is not the problem,their blood father is.