Please help

I came home tonight to a letter saying I have to attend an interview under caution as they have evidence that my claim was incorrect or fraudulent. The only thing I can think of was I did some over time in my last job and I just did a rough guess when filling out my forms. I then started a new job full time last May and rang them a month later to inform them. I got a letter nov/dec time saying I owed them all in all £4200 as they had continued to pay me housing benefit and I got council tax at a reduced rate etc so a family member gave me the money to pay them back which I am now paying them back monthly. But two months later have now received this letter. I am worried sick can't eat or sleep I don't know what's going to happen! Please help

Please help