Hi Steff - As you say you are within your 7 days policy as terms and conditions stated below

10. Cancellation Rights

Where you have purchased the goods or services as a consumer (i.e. for private use as opposed to business use), please note that you are entitled to cancel any contract completed with us within the time scales stated in the below service policy.

7 Day peace of mind guarantee

Just tell them you dont like the phone, it doesnt suit you (you cant get used to it) and you really want to return to what you had before. Just be confident and stick to your guns. I would phone Orange and explain the situation to them to see what they say. Not too sure what would happen about getting your old phone back, Im sure Phones 4 u would be able to explain that to you. If your not one for confrontation then phone them first to hear what they have to say and take a friend with you when you return the phone.