My guess is that they are a debt collecting agency and I would suggest that you treat them as one. What you need to understand is that the Halifax are the only outfit that count and as long as you keep the pressure on them to supply information you can ignore the other flunkeys. In my own case I politely reply to them pointing out that I'm not in a position to deal with the matter since Halifax haven't replied to my requests for information etc.(posted 8042 days ago)If the Halifax don't reply to your SARN within 40 days then report them to the Data Commissioner as advised elsewhere on the site.
TPS are just a tactic the Halifax use (just like Direct Legal & Collections, Aplins etc.) to try to put additional pressure on you. Don't phone them whatever you do, because they really will want to discuss how you are going to pay them some money.