Yeah, those Celestials are total bastards.
"How dare you pay me to help save the universe!"
-- N
Celestials can be bastards- just look at the bible and some other religions. Maybe, your character should have just summoned and asked (that is less presumptous and more respectful than binding). Perhaps, the war is also be taking place on another front and you just pulled one of the soldiers away. There are many reasons why they may not be happy about having a mortal bind them and forcing them into an agreement for freedom.