Incorrect billing on credit card

I am so frustrated with the fact that something went wrong with my payment on my credit card. The debit order came off on the 26th of April and was never included in my available balance on my credit card. The payment went straight out of my credit card which never happens! I called to notify FNB about this and was told everything was in order. My statement closed last night and now I see my available balance is more than R2000 less than what it is supposed to be. I am so irritated as speaking to a consultant is useless as they cannot seem to assist me!!