Topping up £10 gives you 100MB for a month. After the month is passed it eats your credit up in seconds. Ever since I got the phone i have only ever used up 33.11MB.
I installed a statistics app to make sure i would never go beyond that 100MB when not in range of my home router.
This message is made clear and simple so people reading this dont fall into the same trap.
Solution: Permanently turn off mobile internet after that month has passed. Top up when needed then feel free to turn mobile internet on for a month.