Fnb not a business bank and what business saves money and not buy stock

Got an offer from fnb on my app for business overdraft which I app**** and fnb phoned me back after about 2 weeks and told me no sir we can't approve seeing you don't leave funds in your acc so you will not be able to serve your debt if we approve you! I asked him ok how much funds do I need to leave in the account as a balance to whom he could not answer me? I told him it's not a savings account it's a business to pay suppliers and nit there to save money so show a balance! Again he could not give me answers! Shows you fnb is not a business bank cause any business bank will understand money in your account does not buy stock and will def not make your business make more money or make your business grow! In my case my turnover has 10x since I open but fnb can't see that!! Again why will I not have funds in my acc if I know I have debit orders and get a bad itc score! Makes no sense!