If you got any documents or emails from Orange stating their Terms and Conditions then you will have accepted that "you agree that we will begin the provision of the Services from the Start Date and in so doing you acknowledge that any statutory cancellation period and your rights to cancel within that period will end at the Start Date". If you want to cancel after the start date you must pay them all the charges that would be due over the full term. No 7 day cooling off period however Orange must provide their Terms & Conditions via durable medium before service starts for this to be applicable.

See Distance Selling Regulations at the OFT.