@Riddhiman bro please report it to airtel, request u to not keep them in dark on this. In my opinion we should be happy with good offers from airtel and look for cost saving options but causing someone loss at expense of enjoying ourselves is something one should avoid. I can tell u that my conscious starts to question me when i cause even minor monetary or any other loss to anyone knowingly or when it comes to my notice.
Rest i leave upto u, someday airtel will know about this and may call u or visit premise to check, if u feel confident to face them then do continue further but if guilt consumes ur thought then do take the correct call. Just a small advice as a brother, not intended to hurt sentiments or feelings.
Try it once, making others recover from mistakes brings immense happiness which cannot be measured on any scale