If you have linked an Amazon Echo/Alexa unit with a Nest heating and cooling unit here is an interesting bug that I found that you may have come across if you're reading this page here. If you have placed your Nest into Eco mode then the temperatures are automatically set and you can't adjust them. If you are speaking to your Alexa or Echo device and asking her to adjust your temperature it will tell you that the current device is in a mode that does not allow that to be adjusted and to do so please open the Nest application or adjust the settings on your Nest device.
So the only solution is to take the device out of Eco mode if you want to do voice activating temperature changes at home.
Hope this troubleshooting helps.