Good Sams Comenity Visa

I have never been so mad in my life. My husband and I are trying to make a purchase so we decided instead of using our debit card we'd make a big payment on our Good Sams Visa and then use the card for the purchase so that we could get points because we love the rewards. So on 9/11/2015 we went online and paid $5500.00 on the credit card thinking o.k. we should be good to make our deadline of 9/18/2015 for said purchase. Well our card was declined so we called after checking our bank account. The money came out of our checking account on 9/15/2015 so why is our payment not posted so we can use the credit card? They said because it was such a big payment that it could take up to a month for them to post the payment. So O.K no problem could you temporarily raise our credit $3000.00 so that we can complete the transaction until payment posts. They would not work with us what so ever. Very disappointed. We have never been late paying our bill as a matter of fact pay the balance off most of the time.
Am I missing something here!