In that case I take it you put in a new claim in August 2003? If he was working +24 hours you would not have been entitled to IS. I take it you were on CTC at this point?
I'm asking because I'm wondering whether you might accidentally have failed to declare the fact that you were recieving CTC, when you claimed IS?
I'm not certain if they specifically ask you on the form whether you are getting CTC. What they DO ask is whether you have income from any other benefits.
Bascially the only problem here could be if you failed to declare to the DWP on the IS form that you were getting CTC. Now I think that in August 2003 they were not yet moving new IS claimaints onto CTC, but I am really not sure because at that point I was on maternity leave myself. It would be your responsibilty to declare that you were getting CTC. Your IS form will be among your appeal papers.
I'm assuming then that you called CTC to tell them that your partner had moved out? It is worrying that they have not altered your details, I don't see why it makes a differnce who the account name is in, if he is no longer on the claim then he should not be on your award notice. Is his income being taken into account? Also-it sounds like you have a new partner-is his income on the claim? Because you might here risk a CTC overpayment and unless they have massively screwed up (and often not even then) there is NOTHING you can do about this-you would have to pay it back. But this isn't what has happened because your letters are from the DWP, not the Inland Revenue. Also, and a minor point, while his details are on the claim he can access information about the claim. They should take him off for this reason alone, even if it doesn't bother you.
IF you have filled out the claim form and not declared the CTC (and you probably did declare tbh), did your LPA help you? If so, you should be ok as you were acting on advice given by a DWP official. Ditto if the CAB advised you wrongly, and they keep case records-you can ask for a copy of yours-so you can prove that they wrongly advised you if need be.
I really don't want to scare you, I think you should be fine, but do go and see someone with all your bits of paper and get proper advice for your situation.
Good luck!