Refusal to provide Fixed Arrangement Letter

An account of mine was outsourced to ADRS by another debt collections agency. I have an arrangement with ADRS in place, where they are debiting money from my account monthly. I am trying to get a fixed arrangement letter for the account but have been told multiple times by them that they cannot provide me with any letters as the POPIA Act prohibits them to do so because of third party information even though I am the verified account holder. I have requested that any legal reasons prohibiting them from providing me with the letter be sent to me via email and the managers have failed to do so.