Unauthorized items sneaked in

My Mom went to Woolworths Fleurdal Bloemfontein at the food section to buy a few items. NONE of the items she purchased was for clothing. She got the total amount and thought it a bit high, paid for it and then in store went through her slip only to find their was a dress added to her total. When she went to confront the lady working at the till, she said that it happens, it's a computer glitch and that it is the customer's responsibility to check the slip before paying!! Without so much as an apology the lady took R500.00 out of the till and gave it to my Mom! Thus is absolutely ridiculous! I do not buy the excuse of a computer glitch! Is this what Woolworths has become? Sneaking things into customer's totals to have them pay for it?