if they say " why they should pay you", just say, there is labor department and you are going to complain if you do not receive your payment (as you have already left them so saying that will not hurt you). Even say that you will file a legal complain with the help of your lawyer to USCIS. Dhoti ko saato jaan6a ani paisa din6a... yadi dhamkyaudaa pani diena bhane, go and file a complain against them. Bottom line is, you will be paid. Do not worry. Just show them that you know the legal things.