Hey guys, I need some help here, with my killstreaks...

I call the COBRA but when it kills, the death doesn't be added to my killstreak score...EXAMPLE: I call the cobra with 7 killstreaks points, but if I don't kill more using my gun, the killstreak will stay on 7...the deaths are added to game score, but not on the killstreaks to get other item of the ASSAULT PACKAGE... If only the COBRA kills, my killstreaks will stay on 7 until I kill again using my gun...
Someone can help me with this? This starts when I dot a De-Rank by a hacker...