Contract phone not setisfactory

I upgraded my contract phone yesterday, the lady that was selling the phone to me did not give me the opportunity to see the phone before I signed the contract, she only showed me the catalogue, when she gave me the phone it was not what I was expecting, it is not the kind of phone I want, I took it back today and they refuse to give me another phone. I don't want that phone, I cant go for the next 24 months using a phone that I don't like.