Tata Teleservices — legal notice received for alleged unpaid dues

1. I was a long time customer of tata docomo broadband service with account number[protected] starting from 11/10/2014.
2. Till june 2019, i was having that account and never missed any payment. I was approached by sales person of tata tele services for upgrading my connection which i refrained for sometime due to not much need. But in june 13 i accepted the offer after an oral confirmation from the same sales guy that there would not be any change in my rental plan even after upgradation.
3. Sales guy got a form filled from me and got my signature on it which i later came to know to be a new connection request of tata tele services.
4. My old connection was suspended without me getting the new connection for which i raised complaint and came to know about the new connection request.
5. On july 07, 2019 i got a bill of inr522 for my old account, which i paid on july 23. I also got one welcome mail on 1st july for my new connection even though the connection was not done by then by the service engineer.
6. The actual connection was done on 13th july and that too after tampering with my existing intercom connection of my apartment. This led to my intercom becoming non functional for which i raised a complaint with tata tele services without any resolution from their end.
7. I got a bill payment reminder for inr 571 on 14th august against my new connection from tata tele services with account number[protected] without actually seeing any bill in the first place. I raised my concern with the customer care and even sent a mail to this regard on the same date.
8. I came to know from customer care that bill is from 30th june till 14th july for which i promptly raised my concern as the actual connection was done on 13th july. By this time on aug 17, i got a full month bill along with the outstanding amount of total inr 1614. I raised my concern and filed a complaint again as the full month bill was more than my previous connection monthly bill. This was a contradiction to my agreed terms with the sales guy.
9. Since both my complaints were not closed till 29th aug, i kept on informing the customer care that i will not be able to do the payment till they are resolved.
10. I got a service suspension notice on 1st sep from tata tele services after which i requested for a disconnection of my service. I came to know from customer care over phone that i need to clear my dues before disconnection request can be processed.
11. I paid the revised amount of inr1205 on 12th sep to clear my dues for which i received acknowledgement from tata tele services. I kept on waiting for service engineer to come and collect the instrument against my disconnection request but no one showed up.
12. I got a bill for inr1205 on 17th sep which i understood to be a duplicate of my already paid amount. I assumed this to be end of my ordeal with tata tele services but that was not the case.
13. All this time my connection was suspended and since i have requested for disconnection, never used this service. But on oct 7, i again received one more bill which was the most confusing one as it stated a previous balance of inr 982 and current charges of inr 300. I kept on informing the customer care that i had raised disconnection request and cleared all my previous due but to no avail. Eventually the calls stopped and i assumed the case to be closed.
14. On 18th march 2020, i recieved a legal notice (Attached herewith) from sa associates on behalf of tata tele services for the dues.
15.in response to legal notice, i got in touch with appellate of tata tele services, which kept on insisting for payment without even bothering to go through my mails to them.
16. The last response from appellate team informed me that they could not reach me over phone even though i don't have a single call or missed call from them. I have already requested for their number but yet to get a response on that.

I have mail proof for most of the above mentioned. I am also in possession of the router which ideally should have been collected by the service engineer as per my disconnection request. I am willing to hand it over on request.