Did you buy it mail order. If so you have the statutory right to refuse the product for 7 days after receipt in accordance with the Distance Selling Regulations. They must also refund your original price in FULL together with any carriage cost you paid for them to deliver it to you. You must however inform them within 7 days although the product does not need to be with them within that time limit.
They are also breaking the law by selling a second hand item as new. Take lots of photos and take them to a small cl;aims court. You should win on the basis of what you have said and you will get all your costs refunded.