If you file a complaint in the labour court, the case will be decided in your sister's favour. You must create proper documentation. So step 1. Send a registered notice to the company, mentioning that you want to resign for person reasons and the company return your original certificates. Step 2. You should get a reply or get relieved after the official notice period, (which might be 30 days, as per appointment letter). If the end of notice period, send a letter to the Labour department mentioning the facts of the case and request their interference. Mark a copy of the same to the company 99%, company will return the documents and avoid a case in the labour court. Please take help of a professional lawyer, and many are available for a nominal fees. This will ensure, that you do not get into some trap laid by the company