Selling a product without explaining the shortcomings

I purchased a machine on special I have not been treated honestly When we switched the machine on we did not realize that the coffee mug cannot be slipped underneath the opening for the coffee to fall I returned it and they refused to credit me This is very poor experience I have now left the machine at the shop and must request a refund I also offered to pay the difference for a upgrade that can fit the a cup This is a pure way of taking advantage of the consumer