Having been blind sided by O2 with a sequence of bills that amassed to €1003 over 3 months mobile broadband service I think it's fair to say that something's amiss. Digging deeper into this I find that it's actually common place for O2 to be hitting people with €300+ bills for a month of internet service. They get away with it because of an clause buried in their very lengthy and verbose contract that would put a hyperactive buck stallion to sleep.
"
7.1. Monthly Data Usage limits apply and any usage over the limit applicable to your Service is subject to the then applicable excess charge. Where monthly usage is below the usage limit at the end of the monthly period the difference cannot be carried forward from one billing cycle to the next on any Price Plan." But that still doesn't clearly state what will happen if you go over your limit. You have to be very diligent and keep searching...
I have seen it before but honestly at time of writing this post I can't find the bit on the O2 website that states you will be charged 2 cents for every megabyte over your afore mentioned "Monthly Data Usage Limit".
So what does that mean?.. Well that I will leave up to you to figure out.
In my contract I get "10Gb for €20", O2 charge me 2 cents for every megabyte I go over, so how much will the next 10GB cost me?

The meeting point for O2 prey.