Disrespected by the manager and poor service

Today my sister went to Russells furniture shop bochum to enquire about the laybye, she is currently paying for a bed, at first they charged her a certain amount cause they say the bed was on sale, even gave her the papers showing the exact amount that she is suppose to pay. And the price kept on going up, so she went to enquire today, she was told by the so called manager that is not his fault that she didn't check the total amount that she is suppose to pay, saying that the agreement papers that she has, is not the same that they have on the system, the manager was very rude to a point that he said""ga e ye e tsamaye le Mosela wa yona" instead of him taking accountability for what happened, and clarify things.And the sales lady was just sitting there and laughing