Store Card - Customer Service - Incorrect expectations

I went to a store in Zevenwacht Mall and when I tried to pay with my store card I was advised that my card was declined. I was very shocked, when I asked how this can be, the operator told me that I need to pay this month's installment which is only due early next month. I have never skipped a payment before, and made last payment which was due on the 8 Nov which I paid at the same store. I was embarrassed as everyone was looking at me, and probably came across as me having bad debt or me not paying my accounts which is DEFINITELY not the case. The manager was very nonchalant and walked passed me a few times and not once asked me what was going on. As a company who prides themselves in quality, your customer service is lacking big time. It is not my responsibility to approach her but hers to make sure all customer's leave happy and content. It still doesn't make sense as to what the operator told me, as she explained it does not make sense to her as well. What if I had no cash on me to pay for the items? Would any of you be okay with the situation, knowing damn well you have credit on your card but is unable to pay because Woolworth's demand you to pay an installment which is only due early December? I personally feel my consumer right's have been violated and will seek help from the appropriate entity.