Cash back on a Discovery Card Payment.

I made a booking for a hotel on the 23rd April, for check in on the 27May and checkout on the 31May. The Discovery website showed that I would get the 35% discount from Vitality and a further 15% for using the Discovery Card to pay. I continued to make a booking on the Kulula website, the 35% discount from Vitality was allocated, but the 15% for using the wasn't, in fact I wasn't given an option to click on the link to use a Discovery Card to pay. However I continued to pay using the Discovery card, I entered the card details manually, cause I wanted to book in advance and get a booking and be allocated a room, the fare was deducted from my Discovery Card, but the 15% for using the card wasnt. I have contacted the call centres, supp**** proof of payments and bookings. The agent said to me he cant help me further after a couple of days of waiting, as his managers advised him that I needed to produce a screen capture of the fact that I wasnt presented with an option to prompt me to use a Discovery card to pay. I feel that I have been duped, and to some reason known to the call centres the managers arent there to attend to me and help resolve this matter.