Poor customer service

Placed an order online for R237 and successfully paid it using a R50 voucher and a balance of R187.00 from my bank account which successfully went through and the voucher was redeemed. On my arrival at the store (Sunwardpark Drive Thru) for collection i was told that I have to pay R50 that is outstanding and i explained that i have used a voucher and my order was successful, but with no choice i had to pay the R50 they requested making a R237 meal to be R287. Im very disappointed as im used to buying on the Nandos app inclusive of voucher payments.