Airtel Forcing me to pay for a connection which they wrongly installed

Hi,

I requested for airtel broadband connection on 29 sept 2015, paying 6 months
advance of Rs 3857. It was provided in 2 days.
Later after 2 weeks the connection was disconnected automatically and I
received a cheque from airtel dated 05-nov-2015 refunding me the whole amount
of Rs 3857. CHEQUE number - 548380. I called customer care in 2nd week on Nov 2015 ,for reason but the
guy told me we will call you to provide the reason in next 4 hours, which never
came till today.

Now due to brand values of airtel I ordered airtel again for a new connection
on 18 nov-2015. This time I took landline as well as broadband. Land line
number 04040148588 and broadband - 04084753043_ap. I again paid 6 months advance of Rs 4553 till May 2016.

The problem now is that Airtel is called me every alternate day to pay a bill of RS 4070 for a connect which i do not know even.
I raised this concern on 30 Nov 2015. They resolved it after 2 months on Jan 28 2016, stating that there was 2 request which they receive on 29 Sept.
1. One Airtel person directly came to house and taken the advance amount of 3857 - This connection never installed and activated.
2. online request they have taken - This connection was installed

How will a customer know which connection was installed and which not? and Why was i not informed when i called the customer care in 2nd week of Nov that i received a refund cheque for the whole 3857 Amount that this money is with respect of the person who manually took the money and this same connection was never installed and activated. Even the letter from Airtel with refund amount do not mention this . Hence seeing that connection is disconnected, i ordered a new connection on 18 Nov 2016 and again paid Rs 4553 as 6 months advance(this time both Broadband and Landline)

Airtel Claims that the 2nd connection which was installed (as mentioned in point 2) exist till 28 Jan2016, when they actually dig down the reason and forcing me to pay the whole 6 months amount Of Rs 4070 again.

Its not my mistake that:
1. Airtel initiated 2 connection.
2. They refunded me the 3857 Rs without any detailed information
3. No disconnection request i have raised.
4. Must have informed me when i called Airtel on 2nd week on Nov that why Airtel refunded me the amount.
5. When i raised this query on 30-Nov 2016, they should have dig down this problem and root cause and charged me only 2 months money (which i am fine to pay) instead of charging the whole 6 months amount of Rs 4070.

This is just harassment to customer. They have called me more then 100 Times now, while I am in office or driving and in weekends. I sent multiple (more then 30)emails to Appellate/Nodal officers, but no one was listening to me and they do not provide me a higher authority to lodge the complain.

Thanks
Anjan Aich