Default correction

Hi apologies if I'm asking something that has been done a million times. I did start a thread last night but have a few more specific questions on correcting what I feel is an inaccurate and unreasonably delayed default notice.

Firstly, I intend to write to the original creditor, Blackhorse finance and ask them to remove a default notice placed Feb 2012 on a voluntary terminated HP agreement back in Oct 2009. I believe this should have been the date of default. The amount of the default figure is what the balance was in Oct 09 but I made payments totalling £880 through 2009/2011 - so the default figure is wrong too.

Is there a timeline that the creditor must respond to my request?

Should I copy in the credit reference agency at the same time?

Anything else I can do to strengthen my case?

Thanks