you are entitled to a full refund under consumer trading laws as the phone didn't work and they don't have anoither - the model you want.
i also have to say i agree with ethel. if i have problems of this nature, i pick a day where i am not working, go back to the shop and spout off a bit to try and get the refund and if they refuse, tell them i am free all day and will stand outside their shop (on public property) and tell all the customers coming in about their dreadful customer service and non-adherence to trading standards laws. the record (for me) as it stands is telling three customers, before i got a refund, apology and �25 for my troubles. as long as you remain polite, adhere to the law, there is sod all the shop can do. i find saturdays work best, around 2-3pm. have fun!