Unacceptable Client Service

Spar St. Georges in Durban CBD. I was forced to purchase something for a minimum of R50 in order to get a Cashback. I would like to raise a complaint about the service I experienced in this store regarding Cashback Option. In this store if a customer requests a Cashback, we are forced to buy something for a minimum of R50. We are regular customers here and I don't understand why should we get charged for a Cashback. Other retail stores they don't charge customers for Cashbacks. They should declare on their adverti*****t that they differ from other retailers when it comes to in store Cashbacks.