iPhones and Androids are data hogs and they are constantly looking for mail, news, tweets, weather and other updates. All depending on how you have set them up.
A message after you shut off the wifi is not unusual as data usage is not realtime, there is a small lag.
Have you changed the passcode on the mifi from the default passcode so neighbors can not mooch from you?
There appears to be a trend of these threads popping up recently. Perhaps there is a bigger issue at large that has not yet been confirmed.
In the mean time you should do your best to request data logs from VZW, atleast once per month at the end of your billing cylce or as you approach your limit. Checking the reports on the fly would also be helpful, I like to contact the 1800 number and listen to the automated options as my personal preference. That way you have a better idea of how much data is getting consumed and at what time so you can narrow down the possibilities.
Once you have the data logs compare the timestamps of the different sessions to look for any abnormalities or trends. If your MiFi is defective then the logs should reveal consumption at odd hours of the day, perhaps when you are not home, sleeping or away at work. I encourage you to power down the MiFi when the MiFi is not in use to eliminate any concern that VZW has that your device has been compromised and accessed by another individual without your consent.
You have a battle in front of you to proove that the overages are not your own fault. The battle can be won but you need evidence to support your case. VZW typically replaces the devices as thier first line of defence. When replacing the device does not solve the problem then they look to offer chances to get out of the program early.
Please continue to post any new findings that you have as there is a large interest on this topic in the forum.
I have tried to return my MIFI since Sept of last year because it did not match performance described by salespeople. One quietly commented, can't remember if it was at Verizon or on the phone, that "technology is far ahead of ability to supply data." I believe there are enough people having expensive problems with MIFI usage that it is time to initiate an action, perhaps a class action suit, against Verizon. The fact that they refuse to take my device back suggests they are in a very different mode than the usually congenial and helpful one I've experienced in the past. Other ideas?
I bought mine 2 months ago and have tried returning it also. I'm on my 3rd device and still cant stay connected to the internet or get it to load pages when I am connected. When I recieved the first replacement I was told that alot of the issues could be because 4G isn't up and running in my area yet and wont be for about another year. It would have been nice if they would have told me that before I signed up for it. I have to go else where to do stuff for school most of the time. $50 a month down the drain.
VZW will never refuse to take a device back, but they do ask that you pay an Early Termination Fee if you want to cancle your contract before it expires. The default ETF is $175.00. This is an especially hot button issue when overage charges are taken into consideration and users want to get out of the program.
To get compensation for your troubles you will have to battle VZW a little. It takes some work to convince them that the product has not performed as advertised. This means you will have to go through several troubleshooting sessions over the phone and confirm that nothing else can be done to resolve the issue. If you are diligent you can get them to comp or cover the ETF, but it has never been reported on the forums to be a one-call fix or happy experience.