Airtel — existing airtel postpaid plan was auto changed and I lost data that was saved

Hi,
Recently in february airtel auto changed my existing plan.in the sms i received it was mentioned that the plan was upgraded to unlimited calling with 100 sms free. It was done automatically and i lost the 70 gb data that was saved in my existing plan. Nothing related to data was mentioned in mentioned while upgrading to new plan automatically. When i raised this issue to customer care team, they said they will look into this issue and gave me a sr number and the issue was not resolved or addressed. When i called customer care again regarding this, they said they don't have any sr on this and that customer care person was lying completely. Is there anything that can be done to regarding this? I am airtel customer from past 15 years and i feel cheated.