Vodafone — Asking for money without giving any invoice

I was being followed by Vodafone for a Mobile Bill of amount Rs. 597.41, which is completely fake. I was undertaking the service from Voda & ported out to Idea cellular clearing all the previous bills. Now Voda is asking again to pay a bill of the said amount and not in the position to clarify of the same. After asking about the bill, they said since I have ported my no., they will not give any bill.
Now please guide what should I do? The Company wants money without any reason (Unable to produce an Invoice) & threatening for lea-gal actions for not paying the same.