Your mistake is not my problem

Zara has a top I like priced at R199 and I took it to the till to pay for it. Their scanner rang it at R249. The manager tells me that he's sorry they made a mistake but he cannot give it to me for the price on the tag, and that I'd have to pay the R249 that's NOT on the tag...I find this highly disturbing to have to pay an amount that they decide I should pay (sucked off their thumbs, for all I know) and not the price I see on the tag....