I see. And I can see why they only offered a partial credit. It isn't Verizon's fault someone with the password used your data.
BTW, have you looked into Net Zero? It is similar type service, but is advertised as being cheaper than other cellular carrier mifi service.
I love Verizon cell service, but the home fusion and jetpack services are expensive and have a reputation of running up high data use. I'm lucky to have cable internet where I live.