5 months is definitely a rare case. The best is to call Dept of Passport in Nepal again and again till you get someone to talk to. The embassy will have no idea if they in fact haven't received back your passport from Nepal. Did you call at Dept of passport number directly or to ministry of foreign affairs? Phone number of dept. of passport is 4416011,4416012 (Enquiry), 4220108 (MISSION).