Airtel - Incorrect billing for stolen mobile

Here is the summary of the issue -
I have been charged *****/- in my last month's bill. This is due to international roaming charges on my stolen mobile/SIM. I had reported the issue via email to Airtel asking them to block the SIM but Airtel did not block the same. I request Airtel to provide a satisfactory resolution for my issue, else I will be forced to move to a different service provider. It's not possible for me to pay *****/- as a monthly bill. I have also attached a copy of the police complaint I filed in Greece, Athens where my mobile was stolen.
Below is the timeline of events -
**st May -
My mobile phone was stolen in Athens, Greece
I reported the issue through email on airtel *** (please see below). However, the SIM was not blocked.
**th May - I come back to India
**th May - I went to Airtel store, reported the issue and got a new SIM
**th May - I receive a response from airtel *** saying they will block the SIM.
Please note that this is * days after I reported the issue and already got a new SIM. I explained that I have already got a new SIM (please see emails below).
**th June **** - I receive a bill of *****.** for my mobile.
This is mainly due to the fact that the SIM from the stolen mobile was used to make international calls (local calls in Greece) on **st May.