Unprofessional senior staff

Poor service received at Devlands Mitchell's Plain. I do my shopping almost every day. So needless to say my purchases sometimes vary and on several occasions the amount was for less than R50. Now all of the sudden they don't accept card purchases for less than R50. And what further frustrates me is that the Supervisor said it was always this way. I have proof that I swiped for less than R50 in the past. No notifications in store to this effect.