Haven't got any ranked weapon cosmetics

@DoubleyolkXayah seasons 4 and 5, you should've gotten a little Gold weapon charm alongside a Gold Badge. If you did not receive either, submit a support ticket with a screenshot of your rank for both seasons (found under the "view stats" tab) and they'll probably get back to you soon. 

Edit: Attached image for clarity. Under your name in lobby there's a button that says "View stats" click that, it'll show you your stats, and on the right-handside there will be a drop-down that will let you see and select your rank and matching season.