checkers hyper eastgate mall

I went there to withdraw instead voucher. The cashier said their system is slow but he asked me to insect my voucher number & pin, I must go and try to withdraw at ATM. when I get there it says "the voucher has been used". I called the bank and they said the voucher was cashed out at checkers. Went back there, they are saying they did cash out the money. I'm not happy at all!