Tata Docomo — tata docomo - cheating and threatening!

Had been a broadband customer of tata docomo.
In a month, 10+ days it is not working..
In oct 2018, i had paid the bill for the september month but by mistake to another account. I raised a concern and shared the exact details and the account number to which i had paid the bill. They asked for the bill payment details and i had sent the bank statement too.
I was assured that it would be reverted to my account and the issue would be resolved.
However, after 10 days the internet was not working and on asking they responded that it has been disconnected because of non payment.
By october end, i switched to another service and asked them to disconnect.
They refused to disconnect telling that it has been barred! After barring a connection, how do they charge for that connection is beyond my understanding!
Every month during the billing cycle, they keep adding money and send me the bill for payment.
They send 4-5 mails in a day and each time it is a new customer care officer asking the same thing.
I have shared the details and explained to every customer care officer.
One of the officer looked into the bank details and sent that the payment is done in november!! I am unable to understand that they do not even check the details of my account and simply without any diagnosis irresponsibly send emails.
I have even requested to assign a person for this issue and bring this to a logical closure.
I am aware that they are harassing me by doing this.

It has been now 4-5 months, but still the issue is not resolved and have been getting threat calls!!
On informing them of this, there have been no response from their side on the threat calls..
Looks like the team itself calls customers and threaten!