unfair treatment

I'm very very disappointed with the false adverti*****t at edgars the grove, I went to the shop because they had a 50% off on the sale items on the 19th and 18th of July 2021 and the shop was not open because there was no electricity. I asked the staff about when is the promotion ending and I was told it ends on the 22nd of July 2021. I went to the shop yesterday to do my layby and everything amounted to R3000 and I was surprised and didn't want to overeact so when I got home I realise that the 50% offer was not kept as promised so I would like to lodge a grievance at Edgars head office because I feel I was given false hope.