No telephone etiquette from Anthony Richards and Associates

So Anthony Richards and Associates agents keep contacting me and harrasing me with calls regarding an overdue amount. They agents are unprofessional has no way of speaking to their clients and are very demanding. So I have been paying more than what I was supposed to on my sportscene account every month so I was suppose to only pay R550 however I have been making payments of R1300 so now one month of missing a payment i get harrased with calls from fools who has no telephone etiquette no way of speaking to clients and when one ask to speak to a manager the managers are not even bothered. So I'm getting fedup of these calls and if that's the case I'm looking to be reimbursed with all the money I have been paying extra on the account.