False advert on sale

I went to Makgwelereng Mokopane Shell to withdraw money, then decided to go into the shop and buy drinks, So I saw Monstors for 2 with R32. 90,suddenly when I pay they tel me the sale it's over, I asked them why your drinks are still on sale and the advert it's still there, They kept quiet nd didn't say anything to me, The 1 who was on the till insisted that drinks wer not on sale, I said it's fine then IL have to leave them, But Wil report the poor customer service,but she had the guts of asking 1 of the staff member to remove them sale stickers on the fridge