I know what you mean about directly calling a Dean but don't worry, it is perfectly normal here. Also, you could try to call the office and just ask to speak to Dr. Bangash's secretary or personal assistant. If he doesn't have one, just speak to him directly and either ask for his e-mail address through which you could continue to correspond with him or just keep it short and simple so that he doesn't find your call inappropriate.

Good luck and congratulations!