Okay - now I am at my wit's end!

Firstly, thanks to ALL for posting these replies - and to Horizon Hobby for replacing my copter - even though it appears it was unnecessary now.

Latest news - I now have a brand new MCX2 and it works perfectly when using the 120 mAh li-po battery that comes with it. HOWEVER, when using a brand new (tried 3 now) 150 mAh li-po batteries, it will not fly forward or reverse (all other controls work - hover, left and right, sideways, up and down, etc.). What the heck?! How is this possible - am I losing my mind?! I KNOW these copters work with these larger capacity batteries - my old one did extremely well before those batteries went dead. I am ready to pull my hair out and drop kick this hobby to the trash for good. Please - any insight here?

Thanks again for y'all's patience - I wish I was not losing mine...