believe me!! same thing happen to me here in sri lanka with my dialog supper 500 package.it was happen 2004-5 duration.dialog gprs billing system not set properly at that time.so even i download films,software through my computer detail bill indicates that gprs charges for month Rs300-400 only.
so I'm very very happy at that time b'coz dialog providing so cheap solution for IT.
one year+ later i got bill indicates that i have to pay Rs24000 for month and if not they will disconnect my line too. also they indicates that this is ur 1/2 chargers .
so i argued with them with hours by phone and finally went to branch tell them to "this is ur fault not mine,billing system fault urs and y don't u disconnect my line reaching my credit limit" there after that guy called the head i think reconnect my line too.when this happen i already paid Rs6000 to them.
But after two three month later they paid every customer for every cent that they have get from this matter.
i heard that some of customers received Rs85000/90000 bill as their gprs chargers.
that kind of thing can happen anywhere ,to anyone......
br.