Break in protocoll/procedure

I have had an Edcon account since 2006 and have paid my account religiously. I purchased goods on the account in 2013 and when paying the account no outstanding balances where shown on the reciepts. I made my last payment ( according to my calculations) of R500 in April 2013. I then recieved a phone call in August 2014 from a company called CDR saying that Edgars have handed me over to this company due to failure to pay my account. There was an outstanding balance of R210 and arrears of R1600. Before recieving this call I have had no communication with Edgars which is protocol before a client may be haned over to these companies. My details given to CDR by Edgars and they are unable to give me answers regarding their failure to comply with protocol of contacting me. I have paid R250 feeling that this was what I owed them until they are able to give me answers. I am not willing to pay for their failure to follow procedure. I am reviwving harrassing phone calls that reallh upset me because nobody can give me any answers. Would yo please help.