having to repay £1500 of jobseekers they say is overpayment but don't agree

having to repay £1500 of jobseekers they say is overpayment but don't agree I was unemployed between sept 2009 to Feb 2010 after being unfairly dismissed which I won at a tribunal I paid back some of the money to the government then for the time the tribunal covered. i got laid off after only 4 months of work in july 2010 then was out of work till 15 nov 2011 when I took a lower paid job in security which is only paid £6.88 for a 48 hour week and they are still chasing me for the debt know. I have written to my MP

and the jobseekers chief exec what can I do the solicitors have said they will hold off till feb is there a time limit for this kind of debt.

I have asked where the debt comes from to no avail

having to repay £1500 of jobseekers they say is overpayment but don't agree