For those who are having difficulties with Nest and Echo integration, you might want to check where you are setting the name of your Nest Thermostat. There are a number of names, labels, and locations you can set, but Echo only uses one of those.
Here's how to set the name:
Login at Nest.com
You should see a large house icon with the name of your thermostat in large print and the name of your location right below it in smaller print. This is what mine looks like after logging in. Click the gears icon in the upper right corner to go to the settings area.
Here is my settings screen:
At the bottom of the page is the name of my thermostat (it is named HOME).
Click on the name of your thermostat and you can change some of it settings:
Click Where and you'll see two items: Where and Label:
I left the label blank. If yours isn't blank, you might want to consider changing it to blank. Click Where again and you can set the name of the thermostat.
There are several pre-defined names. But I wanted to call mine "HOME" so I typed HOME in the custom field at the bottom.
There may be other ways for the Echo to get the name of your Nest. But the way I just described works perfectly for my equipment, which is comprised of 3 Echoes, 1 Nest thermostat, and over a dozen Wemo devices.
To control my Nest thermostat, I would something say like, "Alexa, set HOME to 75 degrees."
Or "Alexa, increase HOME temperature."
Remember, if you change the name of your Nest, you have to tell Alexa to discover your devices, otherwise she won't know that anything has changed.