Airtel - Unnecessary charges for defective faulty international roaming Airtel services

This is to complain regarding defective/ faulty services provided to me by Airtel during my Switzerland visit. I am hereby providing stepwise details of the whole thing -

*. I have a postpaid mobile connection
*. I activated international roaming for ** days (Rs **** + taxes) on **/**/****
*. I reached the foreign land when I got net connection as well as incoming call facility but no outgoing facility.
*. I complained to Airtel using airport WiFi using MyAirtel app. The complained was acknowledged and I recieved a call saying that they are resolving the issue.
*. To make matters worse by *.** pm local time (foreign land) all connections inclusing data. incoming and outgoing stoped working for me. I again informed Airtel using MyAirtel App using my Hotel WiFi. They tried contacting me but could not as my phone wasnt reachable for obvious reasons.
*. Since my connection did not work I was forced to discontiue this package.
*. I came back to India on **/**/****.
*. I called Airtel customer care and complained about this. The customer care person refused to file a complain stating that it can only be done after bill is generated.
*. I wrote an email to nodalofficer.del@in.airtel.com regarding this. In the mean time a bill of Rs **** was generated including Rs **** + taxes for this aforementioned international roaming package.
**. I recieved multiple calls and emails from Airtel. Intiially they refused to agree to this faulty service. However, later they agreed that the services were indeed faulty. But to my surprise, they are only waiving off Rs **** from the total bill. Also, they refuse to provide me a revised itemised bill.
**. Overall I could use the international roaming for * hours while the package was for *** hours. I fail to undertand why I should be paying Rs **** for such an inadequate service provided by Airtel and that too without getting a revised bill.
**. Because of this faulty services I could not contact my family in time and could not complete some of the important official work that I was supposed to do as Government of India representative during this visit.

I seek your intervention in this regard.
Is Airtel justified me in charging for so much faulty service provided to me?
Should Airtel not provide me a written apology for the discomfort I had because of their unprofessional services?
Are they justified in not providing me a revised itemised bill?
Am I really supposed to pay nearly */*rd the amount for a service which was not even for */**th of the duration (leave alone the quality) promised?
Are customers at the mercy of tlecom companies and their employees?
Is Airtel trying to oblige me by waiving off Rs **** for hiding their incomptency in providing quality services?