If you have been charged more than the original DirectCam Special Offer, this is because the duration of the session was longer than the original Special Offer (it will continue at the rate of the original offer).
You would have seen this confirmation message before being debited/entering:
"NOTE: You will not be automatically exited from this session once the offer duration has elapsed. Once reached your session will continue at the offer rate of x credit(s) per minute.
To proceed click 'OK', to return click 'Cancel'."