Appalling Service by FNB

I don't know why I bothered setting up a debit order mandate on my Credit card with FNB. In December they didn't debit my account, even though there was sufficient funds. To add salt to the wound, FNB sent me a text said to be a "gently reminder for me to pay my account". I was on leave and didn't have the time to look at my transactions, especially those that I have done due deligence by setting up debit order facility. I was even harassed with telephone calls at ungodly hours. This is totally unacceptable, especially if it will have an adverse effect to my credit record. I asked them to send me an email to apologize for this inconvenience to no avail.