Hi
You have tried to obtain a copy of your agreement under the CCA 1974 and so far they have not provided one.
The next step I would suggest is a subject access request(SAR) to the companies Head of compliance (Data Protection Officer). As the request is dealt with under the Data Protection act and not under the CCA, the request is normally handled by staff within the compliance unit. While they handle the SAR, you could request that they suspend collection activity, as you are concerned that they do not have an enforceable agreement with you.
There is a letter under conmankillers post within the following thread which should be ok. http://www.moneysupermarket.com/community/forums/t/sar-template-36954.aspx
The point of making the SAR request is that if they failed to provide a CCA capable of being enforced, it would be difficult for the company to take you to court. From what I have read under other threads, any judge would take a dim view of the company not complying with your requests for information.
It will cost you £10 to make the SAR request but it is worthwhile in regard to the overall process you have started. Even if they don't send you a copy of your orginal agreement, it will show they either haven't got it or have not complied with your proper requests.
As they have applied a default you have a long road ahead of you until the 6 years statute barred period comes up and even then they will harass you. During that time, the debt will be continuously sold on, with loads of letter, phone calls and possibly doorstep visits. Your only hope is that at some point the company offer or accept a reduced amount to settle the debt or you manage to take action via the courts.
Perhaps once you have received the SAR information it may be wise to consider talking to Citizens Advice, Payplan, CCCS or similar for their advice as to the best way forward.
Huckster