Historic debt

Katie51

Hi I received a letter this morning from CSA telling me that money owing to me had been written off as it was not possible to recover the debt. My daughter is now an adult but when she was younger I had to take out loans etc to compensate for not getting any child support. I am therefore much poorer now in my retirement than I would have been as i used my lump sum to clear these debts.
The government website states that the CSA should have sent me a letter telling me that they were going to write off the debt which included a form for me to complete if i wanted them to try to collect the money. If the form was not returned a reminder woud be sent out.
My ex partner is the CEO of a medium sized business and the CSA are aware of his address and national insurance number so collecting the maintenance should not have been impossible. However I did not receive either of the letters. I have tried to complain to the CSA but my case is now closed so I can't get past the loop of putting in my details.
I want to complain to the CSA as i feel they have not followed due process and prevented me from claiming the money owed to me.
Can anyone advise me as to what I should do? Thanks for reading this.