I have had my MiFi 2200 for over a year now. And I've always had a bill around $200. But recently it has been charging me extreme amounts of money ($600-800 bills) and I haven't even been using it that much. I used to use it for online gaming all the time but I have never had any problems like this (can't get anything better internet wise where I live). I barely even touch it now except for facebook and a couple youtube videos. My device has had some bad problems overheating and being extremely slow, also has been dropped numerous times. I've been wondering if its possible that it could have some internal damage that corrupt the usage amount. I'm really sick of seeing insane bills like this. Could it be possible this is whats happening?
There appear to be more reports on data usage than technical issues these days.
The only way to know if your device is defective and overcharging you is to get a hold of your Data Logs from VZW. When you compare the timestamps of the sessions with your normal usage times you should be able to identify where any leaks are coming from. Unusually high usage when you are normally powered down or away from the MiFi are the red flags that you are looking for.
Verizon would normally send a replacement MiFi to you in this situation, but you are most likely beyond the normal support window for your device. I would be careful to power down the MiFi every time I stop using it until the leak can be identified and stopped.