Bad customer service

I went to kfc Elim Hubyeni limpopo to buy meal with coupons that I won from voday shake and win .they refused to sell the food because I was paying with voucher they said I should order online ,I then ordered online and selected pay in store still they refused and they never gave me a reason as to why ,it's feel like they are not trained enough about assisting customers who are paying with voucher .now all my voucher for R150 has expired because they don't want to help us