Poor service ever

I went to Game store in Johannesburg, President and rissik Street on the 24th Nov 2022. The I tem that I wanted to buy was R50 and I have R50 voucher numbers from Game store in my phone I gave the numbers to the cashier then she called her supervisor who tried to enter the number but the system was rejecting she called another person who came and read the message and she told me that to be able to spend R50 I should spend R500, this was a surprise to me because I have receive the voucher after I have spent R500 last week. I ended up not buying the item because I was so frustrated the staff we like if they are not trained or not knowing what to do