Airtel — fraud and harassment

I was airtel cutomer for 6-8 months, ut due to bad service i had ported my number back to vodafone. While porting i had done all my settlements in bill. After 3 months i am getting harassment calls from legal department that i have to come to court for not paying the amount.
The company did not provide me any bill on mail nor a hard copy of rs. 675 and they filed a case on me without even informing me. They say to goto nearest airtel store and do the settlement
As per consumer law which i have studied is never pay your amount unless the bill isn't provided
My issue is why should i do a settle mentunless i am not provided with the proper itemised bill of remaining amount. Why is airtel so afraid of providing the bill and asking to settle the amount

And why was my number ported if the bill was not settled properly. Why should customer goto the airtel gallery and do the settlement rather company providing proper bill to the customer.
For extra usage of 7 days how can my bill come to 675

I had then called the customer care and asked for the bill. The agent said that the bill will be sent in 10 working days. Now i am repeatedly getting calls from legal department giving me dhamki and also from deepak joshi the lawyer of airtel that he will cause my life into mess. And they can't wait for 10 days. When customer service has given me 10 days of period for bill,
This is pure fraud and harassment from the airtel company.