i won the same letter in the Daily Mission !!

hi ,
every time i finish my mission i got the same letter !!! when i will get a new letter ?! i want to get 5 zp crates "Black Market" ,,,,, i though that this thread is important for players don't have zp but for players that have zp they don't care about this >>> who have answer for my question pls post here >>> GOOD LUCK <<<