Misadvised by a MTN sales agent

My mom has a phone contract with mtn and she received a text message in November that she needs to now upgrade and they kept calling her, till I decided that she can upgrade for a Huawei P30 GOLD not any other colour, so they called again, and then this sales lady hungry to make a sale did not tell her that it's not available in GOLD but placed an order for her. Came delivery day which was late December on the 27.12.2019 they delivered P30 lite in Black and she was advised by delivery man that if it's not the colour she ordered she can send it back, which she did but the nearest MTN for us is at Galleria Mall which they said they can't take the phone she needs to return it to the Head offices either in Mhlanga or Pavillion mind due she is disabled and can't walk long distances, but the staff in Galleria said No she needs to go to the head offices, she went to Pavilion MTN which the staff made a mockery of her, asking where on earth she heard of a Gold P30 they were laughing and didn't take her seriously didn't even notice that the order that was delivered to us was not even for us but it was meant to be delivered to someone in Pinetown. MTN is now sending bills that she needs pay 365.and some cents for something that we're not even using, she got a call that phone case is not cleared she needs go to Pavilion again to get a specific number and then she needs to call them to cancel the order??? Why is that?? Why is she paying for something which she is not even using?? She returned the order within the days, it was the sales lady who mislead us thinking we can get the GOLD colour??