Misled on point of sale

I went to Westgate looking to buy a Samsung Tab 7 LTE, I was told at Game store that they can't assist as Cell C was offline. I then went to Cell C outlet to find them operating. I explained to Sindiswa I was looking to buy a Samsung 7 LTE but Game said they offline. She then told me they have it on R59 on promotion. Everything was done, checking and approving. She went to fetch the phone and to my surprise it was notba samsung but a ZTE tab 7. I told her I want a Samsung she apologised sayn she thought I said ZTE. When I enquired about cancelling since I wasn't she convinced me telling m if I'm unhappy with the phone I have 3 months to exchange it with any phone at that cash value. The phone' s headsets are not working. Switched it off and took in today for exchange. When I got there I was told no exchange can be done as this was a promotion. I then requested to cancel the contract was told I will be required to payoff the total value of the tablet which she didn't explain that to me. She didn't outline terms and conditions depriving me of my right to information. The only reason I took it with is because I was told I can bring it for exchange. Shevmadeca mistake not me. Pls solve