LAMBENT COOKIE

i completed the campaign on legendary but the service record says otherwise, i have the achievement for completing the campaign on legendary alone but i have only completed 3 missions according to the service record, i though oh well im not missing out not like i get anything but then i realize i get a set of Armour for completing the campaign on legendary, what is the problem? My account name on Xbox is "LAMBENT COOKIE" if anyone wants to check the achivement can anyone tell me whats wrong?