HANDING ME OVER TO MBD INC

I had a loan account with RCS, I experienced financial difficulties and I ended up not paying my account, RCS then handed me over, To my horror I received calls from two different companies trying to make payment arrangement with me. I then called RCS telling them I actually want to settle my account and they told me i could not settle with them as they have handed me over already, I informed the cal centre lady that I had been receiveing phonecalls and SMS's from two companies regarding my account and that she should confirm which company I need to contact regarding settling my account, She confirmed that i should contact GVDM ATTORNEYS/NEL which is the company they handed me over to, which is exactly what i did, I have settled my account with the attorneys but I still receive harassing calls from MBD, I told the first call centre agent who called me from MBD after I had paid that they should stop calling me as i have paid already, the calls haven't stopped and the final straw was the call i received today from a very rude lady from MBD, told her i paid and she was very cheeky cross questioning me until I hung up on her. Please would you do something about this as I have settled my account.