Airtel — change in plan offers without consent

I am feeling let down by airtel today. I was wondering why my data used to get over very quickly although it was 1gb per month. When i went to airtel sales office, to my surprise i came to know that i was getting only 2gb per month. When i took my postpaid plan i was offered 1gb per day. Now my question is why my plan was changed without my consent? It is also quite surprising that today i was offered a 20 gb per month plan with all other offers same as 549 plan. My question is if the postpaid plan offers are better at lesser price then why do airtel keeps charging a older higher price. Why does a custome have to go and verify the latest offer? If this is the case then what is the benefit of postpaid plan? Airtel ofders postpaid plan of 450 with 1gb per day and similar calls for 4 months. Why cant airtel make postplan remain better compared to prepaid? Going back to my first question, who gives right to airtel to change my data plan without my consent? I hope most o[censored]s complain and file a case.