Overcharged at the centurion branch

Their second edition cataloge advertisers that the prices in that specific cataloge "PRICES VALID AS AT 01 MAY 2021".Their third edition advertisers "PRICES VALID AS AT 01 AUGUST 2021." but on the 20th July they charge me Augusts prices, they said tat the new prices are from 01 August, not 20 July. I phoned them, but they refuse to assist me.