Can you get a DEO from the CSA cancelled?

My partner and I have been dealing with the CSA since Dec 2007. We have provided all the evidence requested and have even chased then up because we had not heard anything from them. After now completing 5 forms and providing numerous wage slips and evidence of myself and my children who my partner also supports, plus getting the run around for the last year or so because this person is not dealing with it anymore and getting passed from pillar to post, we finally get 4 huge envelopes through the post on Monday.

1st – telling us how much we owe from dec 2007 to jan 2009, based on incorrect wages and not allowing for my children.
2nd – jan 2009 to date based on wrong wages but including my children.
3rd – telling us we should have paid an amount 3 days earlier and that because we haven’t (we had no info telling us how much and when!!) they are taking legal action.
4th – an attachment of earnings order to take £122 per week from my partners wages.
After 47 phone calls over the past 3 days and getting passed around again and getting no where we need urgent help.

Can the CSA issue a DEO without warning if no other communication has been received?

Can we get the DEO stopped until we can get all this mess sorted out?

They state that because they have no prior information that my partner supports 2 extra children (which they have had via phone and forms) they can not put them into the equation without “hard evidence” – when asked what they required, they stated a completed form at the time – grrr they have had 5 now!!

How can we get this sorted as we are hitting our heads against the wall here and we can not afford for this DEO to go through as my partners employment contract states that if the employer is presented with a DEO – employment will be terminated immediately. Great no job no money for anyone and we have wanted to pay and have been upfront all the time.

Please help.