Still being called and now negative credit record

I am highly upset with your company at the moment.

I explained to your agents what my situation was and I spoke to a person that granted me a payment arrangement of R500 a month. I made the payments as agreed with now unknown agent of R500 a month but now I was listed as a slow payer and this has now affected my credit score and hence I am now unable to get a home loan. I would like for RCS to send Transunion a letter to state that I did make a payment arrangement and that my account is now in good standing becuase this is now standing in my way of becoming a home owner. I am still being called by your collections department to say that I am in arrears.