I've had the same letters, both dated 31/01 - although my alleged date of default was in April 2011.
Brought up to regard debt as deeply shameful my first reaction was the usual anxiety about possible legal action for debt. However, that very quickly changed to mild euphoria at the prospect of fighting back. I'm worried, of course, and my circumstances are far from ideal - no PC, printer, internet etc and entirely dependent for ICT on the local library, which is very far from ideal but much much better than nothing at all. I'm suffering from depression and under considerable personal strain, but I've never been afraid to fight back and with the information and support available here at CAG and at GOoDF, and other places, I'm going to take them on.
My first act will be a CCA request, then I'll take it from there.