Fishaways voucher bad experience

I had a bad experience today earlier at fishaways I went there to buy a wrap by redeeming my voucher and adding money,the stuff there without name badges were not clued up on how to redeem vouchers they said they can't redeem on thier POS so they could redeem for me on the fishaways app,then I downloaded app the stuff member assisted in redeeming the voucher and was successful on my app but it did not print receipt on thier POS,stuff tried again but voucher now was invalid as it was used on the first attempted order,so after that hole process and being in the store for 40 minutes thier final answer was they can't assist me further as they don't know how the system works properly that's when I had to leave the store with a redeemed voucher and empty handed at Monument park shopping centre.