Harassment and terrible attitude

The person looking after the accounts, Mala Pillay, has possibly the worst attitude I have ever come across. As a long standing customer we have never had an issue before. However, not only I have received the incorrect invoice (someone else, a male, with a completely different name) but I also had to inform her that she is not entitled to contact me almost daily for payment. When I raised the invoice issue via Whatsapp I received an email today from Ms Pillay acting as though I am trying to avoid paying. I resent this treatment and I suggest that due diligence is done when matching names to people and a little training regarding harassment of people who owe money.