Air India — Reg: extra charges incurred for the check-in bag & the harassment caused

This is in regard to my travel from Chandigarh to New Delhi on Feb 05, 2021 on flight number A91 0832 (Air India- Alliance air). I had an international flight to Los Angeles (Separate itinerary) from New Delhi hence I had an extra piece of Check-in Baggage along with me. The cost to carry an extra baggage was around 10, 000 Rupees whereas the ticket itself costed around 4000. I called the air india customer care on Feb 04, 2021 and asked if booking an extra seat on my name would double my baggage allowance or not, to which the executive told me to go ahead with booking the extra seat for 4000 instead of paying 10, 000 more for the baggage. So I purchased two tickets on my name (boarding passes attached) with seat numbers 8C and 8D. To my surprise, the air India officials at the Chandigarh Airport refused to accept my extra baggage saying that an extra seat doesn't fetch the double baggage allowance. Even after repeatedly telling them that I had confirmed this through the customer care, they refused to accept it. I was told to pay ~10, 000. I was in a hurry so I went ahead and paid extra 10, 000 for my extra bag. This was a strict case of negligence on the part of the customer care executives and the Airlines. The troubles didn't end here. 8C and 8D were both my seats. Surprisingly they had resold my seat 8D to another person, despite the ticket for 8D being on my name. This is totally unacceptable, that too in Covid times. This was mentally straining as well. I want the airline to look into this and reimburse the expenses and not mentally tax the customers in future.