Mr Price refusing to take my voucher

I am very unhappy with a service I received from Mr Price in Kuils River, Van Riebeeck. A cashier by the name of Nontlantla said that their store does not take vouchers because of some dispute the store had with a customer before. So apparently their store manager said they should not take vouchers anymore. My question is why sell vouchers and say that they can be redeemed at any MR Price store and then when you go to a particular store you are refused service because of one customer that the staff had a problem with.

Should all stores close down or refuse to serve other customers every time the staff had an argument with a customer? Is that your business strategy? If so then by all means let the public know so that we stop using your vouchers or whatever product that you have "discontinued" because of your bad experience with a client.