Store Manager Being Rude At Pep Mamelodi Square

I was at pep Mamelodi square I wanted to do cash back they told me I should buy something then I said they should give me R5 airtime then they said I should buy with R50 or more to get cash back.. So I would like to know where is it written that I have to buy with R50 for me to get cash back?

The lady who was assisting me was so rude she is the store manager zandi she didn't wanna give me her surname

I want to know why is it not written that I should buy R50 for me to get cash back?

Please attend to this matter