Im her at Van Schalk bookshop Southgate I bought 2 calculators only to find that they are wrong I did tell them that I'm not sure about it but they said I must take them with and return them if they are not correct

Im her at Van Schalk bookshop Southgate I bought 2 calculators only to find that they are wrong I did tell them that I'm not sure about it but they said I must take them with and return them if they are not correct. I took them and got home open both of them ony to find that they are wrong. They are refusing to take them back because the boxes are opened. I went and got a new box for the one that's damaged but still they don't want to take them back..