Got paid current account of business without any loan agreement

Got payment of my works in current account of my business without any loan agreement or any promising note, and get a case against me in ipc 406, 420, 384, 388, 120B and 34 to return the whole amount i received from my client. All money was remitted from my client's current account to mine. I have no purchase order or work orders on my business name for that client, all works was forwarded to my mail, after completion I was used to get the payment. But about after one year i get this case notice , i neither threatened or forced them for remittance but only requested by mail for payment. Kindly suggest What i can do now?