Advertising without stock available.

Since mid January I wanted to upgrade my cellphone contract. They advertise a Samsung A21s that comes with a R4000 shopping voucher. The problem is that they do not have stock since December 2020. However on the 8th of February the again advertise it with no stock available. We urgently need a phone for my son. I cannot get the phone I want with the deal I want at the Retailer of my choice.