I think our "solicitor friend" (who is obviously no solicitor, just a plain 'ol debt-collector), and his comments are not worth all this attention.(posted 8120 days ago)As for the original question, IMHO these people will claim that the earth is flat if they feel it will get more money out of you. Assuming you know his location, could you not ask your ex if he has settled with them.
Until they prove to you that their claim will hold water in court (by providing you with the documents they will rely on in court), then you admit nothing and pay them nothing. Write to them and ask for documents to substantiate their claim, and also ask them for a breakdown of the figure 28000 for account number xxxx, with a further sentence as above for the 23600 on the same account number.
They are likely to reply saying the lower figure was an admin error. this will give you more ammo i.e. Please explain how you can make an error of such proportion (or words to that effect). This brings into question the reliability of any other figures they give you in their breakdown of the claim and the competance of their staff (more ammo for future letters).
Good luck
Stephen