Harrassment of paying customers.

I have an account with Ackermans that I pay religiously on the agreed date upon with Ackermans, however I get constant emails / smses / and phone calls, even once I have paid my account threatening with legal action due to non payment. I have called in and spoken to numerous people, emailed various people, including the person who keeps sending the emails from the collections department. At this stage, i am at the point where I do not want to pay this account and will wait for you to hand me over so I can show your attorneys just how you treat your clients who have agreed to your payment terms. Absolutely disgusting treatment.