Blocking Accounts for no reason

I am an investor in a business which banks with FNB. The business accounts have recently been blocked by FNB and they cannot say why? I rely on my income from the business and without this income I am in dire straights! Have emailed FNB and got a vague reply, however they cannot provide answers and I am disgusted in their handling of the situation. FNB are severely negatively affecting the lives of not only me but other investors as wel, as many of us rely on the income from our investmentl!!!! Shocked and disgusted that FNB can carry on in this way!!!!!!!!