Harassment Award to Debt-in

Harassment is the modus operandi here.I am currently not earning a salary due to an injury at work and am awaiting payments from the WCA for my remuneration. Due to this many of my debts are outstanding.Made arrangements for Old Mutual who appointed a debt collection to negotiate payments with me.After sending all the paperwork and proof we agreed on a minimum amount to be paid.I am still not receiving payments from WCA as tbey have asked for another month to assess.This had been ongoing for two years already. However after I had been paying SSDA,Debt-in called me and told me that they have now been appointed by Old Mutual and no longer SSDA so I explained the story to them and asked them to send me proof that they are appointed by Old Mutual.Immediately after their call I called SSDA who informed me that they have no record of Old Mutual taking away the account from them and that must continue paying them as originally agreed as I had been dealing with them and had agreement with them.Debt-in never contacted me again until now and insist I make payment.I told them on numerous occassions that they should sort it out with Old Mutual and SSDA as I have the POP for all payments done to SSDA.Still they are unable to.understand that this is NOT my fault and I am paying SSDA.I get calls every hour from Debt-in.Dont they understand English and the email they gave me gets rejected by google as possible phising site.Now what do I do