Dryden79,
I have just read your post again, the bit about being a rubbish dad etc etc no money, no food it sounds a terrible situation!
My advice would be not to worry about getting money out of the ex, but to get yourself sorted out with a regular income so you can look after your daughter, feed, clothe and house her as she is the most important thing right now… Isn’t she? I’m speaking from experience but this money that is owed to will consume you and take over your life so I would forget about it for the minute and just concentrate on looking after your daughter and getting yourself settled.
What would be easier is just to right it off, forget about it and move on! Sorry for being blunt but i have been where you are twice now and it does take over your life!
Good luck