False Advertising re Cash back offer terms

Decided to take advantage of an advertised “cash back when you upgrade” deal. Terms stated & Store confirmed payment in 48 to 72 hours. 4 days later I try to enquire what is the delay only to be told by a “sales agent” they don’t offer cash back! Then she agrees they do & advises it takes 7 to 14 days! Contrary to what is advertised? Store manager contacts me apologising & assures me finance will expedite, further promising feedback the same day. That feedback never came, neither did the payment. I make contact again the following day only for another store manager to contact me and inform me that finance has communicated it’s too close to a weekend so they cannot do anything. What happened the previous day….nothing? Absolute shambles of an experience!