I want my 3500 voucher that was advertised with the package simple

I ordered a laptop online on mondo at Vodacom and the laptop was suppose to come with an HP voucher to the value of 3500 and I received a voucher of 300 as I was told when I was activating it to buy at homemark and I called them asking were is my voucher they tell me that they don't know about the 3500 voucher they only know about the 300 voucher then I was transferred to the supervisor she told me I must qualify first then I asked her how was I not told about that otherwise I would have just bought the laptop on it's own and the router this people cant even come up with a plan to solve the problem I mean they are just a bunch of liers and for the falls advertising they are doing they are desperate to make sales