Wi-codes and vouchers

I'm so disappointed with Pavilion store. I had a voucher from vodacom to use, however I was going to add cash to complete the order. After trying to reach their landlines and find out how is the voucher used their line was engaged. I walked to the store only to be told I cannot use the voucher in store I have to order online. Where does it state that all WI codes and vouchers are only redeemable for online purchases. My voucher expires soon. Please note that I Do not have space on my phone for the app.