not too sure how you can go about cancelling the contract tbh without paying it up

how long is the contract for?
i have had the same issue with the orange safeguard, just not as many times as you

I also use my internet at home through on of there orange dongles...this also from time to time will revert back to saying that im under 18

all i have to do each time is phone up tell them it has come on again on a car forum site which is not over 18 rated and they turn it off again! takes the piss that it keeps resetting itself but luckily it doesn't happen that often for me! It does happen on my phone too, not just on the dongle so i can relate to you on that!
There customer service is appauling, nearly every month they have over charged me somewhere along the line, and when i had an issue with my dongle where i couldn't connect to the internet at all...after making me drive 11 miles to a mates house knowing they had a dongle and trying that to find that it worked, they then made me delete bits and pieces off of my laptop to "solve" it which didn't happen, they then suggested i go to the store, so 11 miles back and into the store i go, took my laptop with me and the store couldn't understand and they rang up the same people i had just spent 5 hours dealing with, who still didn't have a clue what they were doing. In the end the woman on the phone agreed to send me a replacement dongle by the next morning on "good will"....next bill comes in with £70 charge on it for the dongle replacement

just one thing after another with them tbh!
hopefully you can find a way out of the contract and update us as to how! lol
good luck
x