DWP Benefit Debt

Hi Folks,
I desperately need some help with a letter I recieved recently from the DWP stating I owed them money from 1998. I wrote to them twice asking them to prove that I owed this money and I also pointed out to them that in or around 2003 -2005 I paid them back almost £700 in installments for the debt they say I currently owe. I had to send a recorded delivery letter to them and got a rspnse yesterday with 2 print outs showing the payments I recieved which totalled almost £700.00. The letter states that I owe this money from 1998 but that they do not keep records of repayments from more than 2 years ago, how absurd is this.

On top of that a Debt Collection Agency called Frederickson International are constantly writing to me and calling my phone. In my letter to the DWP I told them that this company was causing me severe mental distress but in the DWP response they say they have not called in this Debt collection agency, however the figures qouted by the DWP and the figures qouted by Frederickson International are complete matches.

I am at my wits end with this and am getting to the point where I feel almost suicidal over this. I currently recieve DLA and try desperately to hold down a job whenever I can but this situation is now affecting my health adversely and I have been unable to work fort he last few weeks, and no work means no pay so I am finding myself on something of a hamster wheel.

I'm not disputing that I receieved government moeny but I know I paid it back after coming to an agreement with the DWP all those years ago, Can someone please give me some advice on this before I get to the point of crawling under my duvet and never coming back out please?