Standard bank cheque account

I had an account (cheque ) with standard bank then I decided to move n use another bank without closing my check account with standard bank (I wasn't aware that I had to Close it) on the 29-06-18 I received a msg from their lawyers telling me to pay my areas with standard bank on the 30-06-18 then I called them, I wanted to understand which areas cos the message was like a shock to me

Then my worry is why did they sent me to their lawyers without letting me know cos I never received any messages, emails or a calls from them n why did they wait for so long cos as it for now they are telling me that I'm owing R2900

I think on that they violeted my rights as a customer

Help me out please