Online purchase declined by bank and 3 hours and 5 agents later, I am no closer to being able to complete my purchase

I have been trying all afternoon to make an online purchase using my business card and keep getting the following error message: Unfortunately your order cannot be processed as the originating bank/merchant has declined your transaction. Please attempt your purchase again. I have been chatting to FNB's agents for almost 3 hours now and the issue is still not resolved. I have been transferred to 5 different agents, keep getting disconnected. The last agent told she had resolved the issue and I must try again. While I was trying again, she closed the chat. It still gives me the same error message and now I have been sent to the back of the queue after 3 hours of trying to resolve this. It is so frustrating. Such terrible service.