Can I return my contact phone from Go Mobile I got yesterday as iv changed my mind?

[Gemma]

Took a contact phone out yesterday and got really confussed when taking it out cos the salesman made me think it was a better deal then I really is, got home changed my mind and went straight back to the shop thinking I have a 7 or 14 cooling off to be told I can't return it!!! Is this legal???? Just to add the phone has Not been out the box!!! Thank you please help me!!!! X