Poor voucher system

I tried to use a R100 voucher gifted to me via computicket. The sms said it could only be used once. Bought 3 items total R98.70 and produced the barcode only to be told it must be more than R100. I had no cash on me to buy more. I explained to the cashier and then manager that nowhere does it say I had to use over R100. After an embarrassing time and glares from other customers the manager eventually fetched R5 and added a small sweet. So you need to say the voucher is for R100 or more. You try and make up articles to end up on exactly R100!! Many vouchers are given to the needy who might not have a cent more than the R100 voucher.