bad service and bad attitude

Went to McDonald's today to redeem my voucher, got to the cashier named Akon, firstly he complains that my voucher amount is too small and McDonald's should not accept such vouchers. I was shocked and disappointed but i kept quite. He calls someone to help him redeem the voucher, whole time he is processing my voucher he is giving me attitude. He never asked what Big Mac burger i wanted, only his colleague asked about my order. But still i maintained my cool, bcz i know am crazy as hell and i don't want to show people that side of me. Then i completely lost it when the order came and it was not what i ordered. Had he not given me bad attitude before, i would've waited for them to fix my order. I redeem my vouchers every month at any MacDonald here in East London, and i have never come across such bad service. On top of that I am a loyal customer at MacDonalds for years now and i've never experienced such bad treatment and humiliation. Some take that Akon guy for training on customer service otherwise he's gona ruin your reputation. I am still angry as i'm writing this.