Thanks for the suggestion. I have unplugged the device for more than 15 minutes and it hasn't made a difference. In the last 24 hours it has used 293 MB. I checked with support via chat and got
"I would like to inform you that, all the echo devices doesn't have a screen and inbuilt software in it. Also, there are no pre installed applications on the device so it just uses the wifi sensors to connect with the application hence the bandwidth consumption would be very less when compared to the echo spot. As echo spot uses the screen and backend application always run that is the reason, it uses a huge bandwidth."
So I asked to return the Spot and he was nice enough to issue me a return. He also said he would have engineering look into this.