The 'ECO' mode has nothing to do with your voice mail. It means the phone is in ECOnomy mode and therefore using less power. What happens when you are near your base unit so that high power is not required.
As for the calls suddenly going straight Voice Mail, that means you somehow enabled your VM service with your phone company. Or someone else did. That is not a function of the phone. It's handled by your service provider. Once you disable VM, the calls will come through again. You can control that setting by logging into your account. Call your service provider if you need help with that.