Promotion that the cashier didn't know and the manager said it was a wrong promotion date

There was a promotion that when you buy two Viennas you get a lunch,so I bought them and the lady that assisted me said she knows nothing about it then sent the other lady to check it and the lady came back to confirm am telling the truth,so the cashier sent me to Lesogo who happened to be the acting manage on duty that the ,I tried explaining to him then he gave attitude and said the special only starts on the 15th,my question was if the front Vienna's expiring date is on the 15 is it possible that the special can resume that day he continued to say that thes pecial is for the 15th January ,my question is if that is the case why was it not labeled on the promotion.I tried call pick and pay customer number with no luck and then I wrong to to them and I haven't heard anything from them.