Disappointed by Pick n pay

I received coupons from Deals4u and when i had to reedem them at Pick n Pay, the one in Rustenburg town the cashier told me that they know nothing about the coupons and those things gives them hard time so my question is, why are we receiving these coupons and they make it difficult for us to reedem them, do you know how embarrassing it is to stand in the queue only to look like a fool...why are the cashier not informed