job seekers overpayment

Guyz I'm in need of some help or advice about job seekers overs payments. I had lettes from the job centre saying they over paid me £1050 back in 2011.I first received the letter I think it was in 2012,when I received I made the appeal as Im adamant that I did nothing wrong.They said they over paid me between 23 October 2010 to 4th March 2012.When I first signed on the jobseekers I told them I was working but I was working 11 hours a week and I was told that it's not a problem aslong as I don't go over 16 hours and every two weeks when I was going to sign on I was asked to bring my payslips, if I didn't or forgot my jobseekers was stopped straightaway so I wonder y did it take them so long to realise I was being over paid and according to what they said to me when I fist signed on was aslong I don't go over 16 hours,now they have asked debt collectors to get the money for them.I have rung the Dwp they say I need to talk to jobcentre that dealt with my application, I have rung them them also have said I need to ring their credit depart who in turn say ring the debt collectors as the case is no longer with them.
Pliz anyone know who I should call or assist me having this heard in court cause at the moment I'm just hitting a brick wall and the 084 number are costing me a fortune