Change of Phone

i just took out a contract on Friday 9/07/15, i'm not happy with the phone so i want to change it to another with a higher paying contract. I phoned in on 13/07/15, the sales person is utterly rude and keeps telling me what is good for them they are always giving bad service. they say i can lose my number and cant give me a guarantee as to when i will be able to retrieve my number. now I'm stuck with a phone i don't like and cant cancel the contract. which there is a 7 day open window period ********!