What is this??

About a month ago, I went into an Edgars Active in Rustenburg with an intention to layby a sneaker. I got there & there was a sale on, so I took two instead because, like other kids, I wanted to save, so why not? Besides, it's allowed & the payment condition still stands & one pays for the price that was marked on the item when they decided they wanna purchase it... I mean, it's happened before. Everything was punched into the system, gave money, got a receipt & left the store. Now a month later, all excited with built expectation that I'm getting my new sneakers, I get into the store with the balancing money, I pay. Now the person assisting me asks for a void from the manager I'm assuming, to be done because again, they're not used to the system doing whatever it is that it was doing. To cut long story short, then bham, I'm thrown with news that, either I have to pay double the amount that I had in my hand because it was the balancing fee on their system, or they give the money that I had already paid out back... I'm told I'm actually the second person to some into the store to experience such & what I'm picking up from that statement is that, "don't look at us, it's not our fault & we can't help you". But now, that was not the initial agreement with them... I never said I want my money back, I mean, I came for sneakers & I was expecting to come out with sneakers from the money that I had in hand. It is uncalled for! Why then if your system does not allow sale items to be bought on layby, does it not kick the the user out as so not to build expectations as soon as they punch in layby on sale date? And since when are sale items not allowed to be bought on layby as it was possible before? Who was informed because clearly the employees also had no idea whatsoever? I cannot be paying double of what I was expecting to pay. I left the sneakers in the store & refused to take the money because that ain't initially what I came to do. Please Fix this.