Money credited wrongly to my trading account by broker

Hi. My stock broker sent me an legal notice saying they have credited my trading account of around 1 lakh due to technical error. Now they are asking me to pay back that money and intentional fraudulent action by me which is completely untrue. My family member had an acc with them and similar thing happened and deducted money from her trading acc, so I got worried abt their efficiency and withdrew money from my acc. they processed that withdrawal request, verified and transfered to my bank acc. I wasn't aware of those. But when they sent the ledger it seems they credited that extra amount and I had withdrawn that money long back. So what should I do because I don;t have al;l that money to pay them back. Thank you.