Misleading Advert

I was mislead by the ad claiming that if I download the app I will redeem the voucher if I order online. I did the order the voucher was invalid and I proceeded to the order and collect to redeem the voucher when I pay in store unfortunately that was not the case when I got instore nobody had a clue and I asked that they called head office I was told to call headoffice myself since they are saving telephone cost for the company and that head office does not entertain such quiries. I felt that the service was very much unfair and very misleading.