Freedompop Fraudant usage charges Los Angeles, California Nationwide

Signed on in 2011 and used Photon device which was fine except the some limited coverage areas. Their usage and charages seemed to be fair as expected. Last November the company decommissioned the Photon now I am forced to use Netgear Mingle device and here are problems:

i noticed at times 1mb to 3mb usage were charged every few minutes when I knew that I was at home using internet instead of Freedompop wifi. I called the company and was told that in order to avoide the charges, I have to turn off the device even I was not using the device for wifi. That was new and a shock, have we ever need to turn off the smartphone when not in use? i did not believe them so this morning I turned the device on whil in a doctor's office and left it on without accessing the internet until I return home after one and one half hour later, I checked the usage and was shocked to see that I used the device 10 times, about 130 mb was used, for nothing, never happened when I was using Photon device. My plan is so called 500mb per month, so for 90minutes simply letting the device on I burned more than 25% off my monthly "free" allotment. Really? This is a ripoff.