staff not aware of promotional discounts

i went to jet mart at randburg square to do a purchase, the lady at new accounts told me about the 50% off discount on your 1st purchase when you open an account, i was very interested and opened the account which took about an hour as their system was very slow, i came back later after checking my application through customer service. i asked if i can buy a phone and they said no the discount is not for phones, i went to take clothes and when i was about to pay the old lady kept saying she doesn't have vision and they kept assisting other customers while i waited for about 30 minutes to get assistance, after the wait they scanned by staff and told me i only qualify for the booklet discount which was not even 20% off, i told them about the 50% off discount and they said no they don't know anything about that, they went to ask the store manager and she also said she does not know of that, i showed them special on their website on my phone and they said its false advertising, no one was willing to help and they were saying its the 1st they hear of this, i ended up looking like a fool in a store full of customers, they didn't bother to call head office to find out.