Extremely Poor Service

After my credit card was declined for a purchase in the US last week I have been trying without fail to sort it out - because there can be no reason from my side that it should have been declined. Having registered a complaint on the FNB website, complaint reference number ***F, I have heard from no one. Not a soul, and now my credit card has been declined again. What does one have to do to get FNB to sort things out. I have had nothing but extremely poor service from FNB since a burglary (and having to cancel cards, etc) about a month ago. Nobody seems to know what they are doing, it is a nightmare and possibly now time to move my Premier accounts to another bank.