I have shredded it , stupid me I thought the issue was resolved. But I can get bank statement showing that they repaid me, do u think that can help

I received a letter confirming that i have to attend the interview and advising that interview will be take place under caution (which I don't know what it means) also letter stated that ` we have arranged this interview because we believe there are grounds for suspecting that a criminal offence may have been committed ` The issue started back in July 2012 where some one claimed Social Funds using my name and details. Since then I have been in contact and I have provided them with all identification to proof that its not me. They sent me copy of the applications completed and they all had different signatures which of course did not match my signature. So finally around Feb 2013 they stated that they will stop chasing me as they believe it was not me . At that time of this ordeal i was on JSA and they were deducting money from my allowance which eventually they repaid me when they withdraw their case and i started my full-time job on 3rd of June with DWP. I am really nervous never been in such situation before as I have always been good with my credit history, Can anyone advise on what will happen on the day of the interview and what should I expect