Overcharged and bad attitude from msnager

Went to usave store at 226 Francis Baard street pretoria (S034304 R03) on 28/02/2020 and bought about 22 items. On the items, was 3 domestic bleach which the prices on the shelves was R22.99 each and handy andy was R18.99. I realised on the 2nd of March that I was overcharged on the receipt because a colleague wanted the items and was asking how much was it so I gave him the receipt to check. Only to realise I bought them with its normal prices. I shouldn't have bought many if it was not on special In fact i shouldn't have bought them at all. I went to the store on 3rd with the receipt. Spoke to the security guy who referred us (me and colleague) to the manager. Yooooo the attitude of that lady is rotten, lack of leadership s****s. I didnt even know she was the manager. She told us that each time we buy something we must check on the screen the prices while scanning the items, for heaven sake I bought 22 items, meaning I should check all the items if the prices are the same as on the shelves. She said I must return the goods so that she gives back my money with a very bad attitude. And this is not the 1st time I encountered something like this from the same store. Few weeks ago I bought pack of 3pencils, on the shelves the price was R14.99 but at the till it was R29.99 luckily I saw it before I left the the store. I called head office and spoke to Jullian ref no:283502. He tried calling the store since on the 3rd until today the 4th and no one is answering the phone. He then told me to take the items back to the store. This things are heavy to be running around with them. I have the receipt why cant they just give me the difference of which I was overcharged.