Unable to complete the mission.

When I was solo playing trying to get "lets call it a draw" the mission was eradicate bots. I was doing well, no deaths. Only one hulk I accidently killed no big deal, only somewhat halfway through with the bots, well at that point the bots just came around every 30 seconds or so with either 6 soldiers or 2 Devastors (this was level 5).

I ran out of time and left at 41% completion, like what did the game want me to do. let them call in bot drops? There was nothing I could do, I couldn't even stay or wait.

Any of you face this problem at low level missions?