poor customer service and no product knowledge

after weve asked so many times if the 3G routher is the right one for the purpose we want to use it MIchael confirmed yes. to our surprise it wasnt. so we took it back today. the sales lady that helped today come everytime with a different story. that it is wrong. then no the technical department say they will set it up. then came back and said o but theres a call out fee I said excuse me I must pay because you gave me the wrongt product so how will you set it up. Samantha the sales manager didnt once speak to me why do you take of a 15% of a refund if you gave me the wrong product. then the sales manager asked the sales lady if she is okay forget about the client that is standing there. there staff dont have knowledge of the products and the customer have to pay for it I want to know where does it state that you take 15% of if a client got the wrong product because of a sales person given the customer the wrong product. And what is the sales Manager suppose to do. as a customer we trust the sales person and expect them to help us. how can you charge a customer a percentage for returning a wrong given product in the first place.