Poor service

So I've had an account with FNB for almost 6 years and the last couple of months my account has been going into an overdraft where I never signed for or app**** for an overdraft. As a result, transactions are not going off when I swipe which goes to an overdraft and eventually mounts up thousands which is then taken from my next deposits. I'm being threatened by calls. This is very unpleasant and I'm sad to say but I'm moving my banking and business elsewhere.