Call them at 9am, tell them you've only just seen the letters last night and ask if you can arrange some sort of repayment. A little each month on top of you normal payment. Try and find out why the DD was cancelled too, it could have been some stupid arse from their end.
I too recieved a threatening letter from the council this week telling me they were taking me to court, you wouldn't believe how many times I've arranged payments and it's just not gone through, I end up keep on making payments over the phone, after this week it's hopefully sorted though!
Good luck with it CUS anyway, I hope you get it sorted quickly, I'm sure you don't want it hanging over you this weekend!