rewards voucher invalid

I won a reward of a r10- Shoprite voucher. I tried to claim the prize at Shoprite but the voucher didn't go through. I paid for the items cash out of embarrassment. Then I called Cell C to query why the voucher didn't go through. The person on the line told me that the voucher was valid from his side and advised me to go to another store to claim the prize. I did so and again the voucher did not go through. Again I paid for the items. The query was escalated and I was refunded the r10 in airtime. I asked the agent on the phone, if they could not give something better for the time, effort and embarrassment trying to retrieve the voucher caused me. so said there was nothing that she could do. So after all the effort of going to two different stores, having the voucher declined and having to pay for the items from my own money, Cell C simply rewarded me a r10- airtime, not even for inconvenience, but because the voucher didn't go through. I find this to be pathetic service on the part of Cell C.