Being duped and misled by Pick n pay Festival mall

I am unhappy with the treatment I got from Pick n pay festival mall in kempton park, they gave me a voucher that says R100 off your next shop at pick n pay festival mall, so on my next purchase I went there with the hope that I will get R100 off of my purchase but I was told that I should have bought R400 or more but the voucher doesn't say that.

It's like we are being duped into purchasing there only to be told that your voucher is for R400 or more, they should have specified on the voucher.