McDonald's App Voucher fail!

I would like to complain about the so-called vouchers that are on the McDonald's App. On Sunday 22 April 2018, my wife, my son and myself downloaded and installed the App on our phones. We decided to make use of the great offers and wanted to try out the Double Boerie Burger for 90c. We went to the McDonald's in Vanderbijlpark and my wife ordered her burger and also some ice-creams. When she wanted to pay and redeemed her voucher, the cashier told her that it is not valid and we called for the manager. She also said that it is not valid in Vanderbijlpark. We told her that this coupon or voucher is advertised on the App but she insisted it is not valid. I phoned the Vereeniging branch and the lady there told me that the coupons must be loaded on their systems and they have been asking for it but still waiting for this to be done. My question is this - how can these vouchers be advertised and then it is not accepted at certain branches. Just yesterday, my other son made use of his voucher in Menlyn Mall, Pretoria. My wife also lost her voucher on this offer as she redeemed it at the cashier but then the order got cancelled. I am really disgusted by this as this is false advertising!