Vodafone Idea - Harassment calling

I was customer of Vodafone few years back. I was using the network some time and I had postpaid connection. But then as the financial condition of company deteriorated and it led to merger of the company the availability of network also deteriorated significantly. Despite all my complaints there was no improvement meanwhile during all this time company was charging regular billing and I have paid on time. But one fine day I cleared my billing and I moved to new network. I am happy with new network but then one fine day may almost after two years I received call from Vodafone Idea asking pending payment of one month despite me clearing bills before shifting. Now almost for one year they're torturing me with continuous calls and threats of CIBIL & consumer Court and what not. They are literally harassing sometimes they are as they from CIBIL office. I suppose more than **-**% of their customers must have shifted and they may be treating everyone like this or instead paying damages for their faulty network and forcing them to shift to other networks they are looting money from customers strict action must be taken against them for mental harassment.