FNB blocked my card without my consent.

Today my account got block by FNB, I don't know for what reason they have decided to block my account without my knowledge. I was not able to buy my sick son medicine because of FNB decision of blocking my card. I wrote to them to resolve this matter but still nothing, I didn't even got a response from them . Can FNB please unblock my card and give me my money I will find myself a bank that knows to communicate with it's clients and not put them under unnecessary stress. I have been banking with FNB for lot of year now but I feel that this bank is taking some of it's clients for granted.