It is clear what he wanted, and it is clear what devry was trying to do. He wanted you to pay maximum amount for a service, which is his right. He told you, you could pick the quests and you told him he could pick. Which at the end of the day is your fault. Yes you thought 25M was going to get you to the required QP, but he clearly told you he would do "25m" worth of quests. I can't really force him to do anything, other than be more careful with the wording next time.
I hope Devry can understand you were under the wrong impression and help you out for really cheap, but I won't hold him to this. It is up to him, dispute closed.