Draw Calls Not Reduced After Adding Texture Atlas.

I'm working on a simple mobile 2D game. Currently there are 20 draw calls. To minimize the draw calls number, I put all the graphics into a Texture Atlas using the Sprite Packer. I expected a reduction down to about 5 draw calls. Surprisingly, I'm **not seeing any decrease in the number of draw calls**. I tried to replicate this scenario in a clean project and everything works as expected. So, this is probably not a Unity bug, but rather something in my original project that is preventing Unity from optimizing the number of draw calls. Any suggestions how to fix that?