Your heroes aren’t optimal for those levels to get 3*. At least how I beat 11-9 and 11-10 to get 3*. I ran Dogface and 4 tanks that can heal or gives a shield. I believe I used Dogface, Phalanx, Heimlock, Matador and Mandrake, and just blasted the helios/objective heroes with Dogface.
I actually don’t remember how I got 3* on 12-10 might have been with the Mauler, Halo and Ifrit combo before the nerf but I could possibly have used the same comp as I did with 11-9 and 11-10.