Dishonest advertising

I just tried to upgrade to a Huawei Nova 10 Pro at R349 per month for 36 months, the deal was on an adverti*****t on the counter directly in front of the consultant helping me. No mention anywhere on the card of T&C's apply, no mention of E&OE, nothing of the kind. Yet the consultant said it was a mistake. She contacted her manager, who was not in today, and he apparently said they cannot honour the deal. Surely if the deal is advertised in full public view the deal should be honoured? This is like seeing a price on a supermarket shelf, and being charged a different price at the till, they honour the advertised price. Anyone have any advice, cos I am sure that card will be destroyed by now!!