Shocking Display of professionalism

I have been in constant communication on the bill outstanding. It is because they neglected to submit directly to the medical aid we now sit with an outstanding amount. I had to get all the codes and liaise with the medical aid for payment. Inspite of this, I get a letter from their attorney.

Today I get an email from Siyabonga Mbatha that starts the email like this '.Please understand ER consulting practice of Drs. Holt and Partners expects all ...'. Yes the beginning of the sentence started with a full stop and sounds more like we in a street fight rather than a professional email. Further, the bill attached to me is in credit. Blow me down for sending me to their attorneys if they owe me money.