Airtel — Plan changed without my knowledge

Address: Chennai, Tamil Nadu

My Airtel account number is 13939021. I was in a plan of 1099 40Gb for 4mbps speed and I use to get 250 rs discount every month since Airtel promised me my bill wont cross above 1050 rs. Airtel offered me 1099 60gb plan for 4mbps speed, I worte an email to them stating not to change my plan as I am happy with 1099 40gb 4mbps speed. Even after writing an email they changed my plan to 1099 60 gb 4mbps speed and they deactivated my 250rs discount and replaced it with just 100rs. I am using this connection from past 8 years, when I emailed them again they say its our mistake but we cant provide you more than 100 rs discount. Without my knowledge they are changing my plan and deactivating the discounts. I wrote 3 mails and got no satisfying reply. They are ready to lose a customer for the mistake they have made. I did not expect this from a brand like Airtel. They are unfair to their old customer. All I want is give back my 250rs discount. Thats it. This is a mistake from your side, not my side.