For clarity, CST can't take legal action on behalf of DRP, DRP don't own the debt - they have no 'interest' (in the legal sense) in it, CST can only take legal action on behalf of Smart if they were to do anything.
This is all part of the standard 'half truths' threatograms they send. Of course you would only have a relevant CCJ IF they took you to court, IF they won and IF you still then don't pay in time. They don't just get to apply for, and then receive, one.