Since updating to Marshmallow, my cell phone is useless as a phone. I cannot make or receive calls because I cannot hear anyone on the other end, no matter if I call them or they call me. Well, in fact my phone doesn't even ring at all anymore. It goes straight to voice mail. The only way I can hear my messages is if the ear phones are plugged in. If I don't plug my ear phones in to call voice mail, I cannot hear it ring or a message or anything. It just hangs up on me. If I call someone without the earphones plugged in, they cannot hear me and I cannot hear the phone ringing on their end or anything they say, not a message or anything. This makes my cell phone useless as a phone. TOTALLY UNACCEPTABLE. I want to revert back to the previous OS, but cannot find a way to do so. I called my cell phone provider and they had me do a factory reset, but my phone still had Marshmallow and although the speaker started working properly for 2 or 3 calls, it is again not working and I am not willing to put up with this useless OS. Please tell me how to revert back to the previous OS ASAP. I NEED MY PHONE to work as a PHONE!