exchange not accepted

Bought tiles on Tuesday but noticed today (Saturday) that the color differs. When approached store one of the sales ladies there said that papers for Tuesday have been thrown away. The store manager (Jan) said he can't help since we don't have proof of payment ofwhich that should not be the case because with time, barcode, total amount paid and date, a proof of purchase can be retrieved from the system. When I told him about this he said he will speak to the Regional Manager. Few minutes later he said the Regional Manager doesn't approve the exchange. This is totally bad customer service. I even confirmed with the other store and they said its possible.