Airtel — providing customer details to third party - misuse

I bought a 4g wifi dongle with postpaid sim in airtel showroom t. Nagar during the month of august. I received a call on 24th nov, 2017 from balasundhari[protected] stating they are calling from airtel. They told me airtel is offering prepaid connection for postpaid dongle users also have good offers. They told they can come to my place and activate the prepaid connection and for first time recharge you have to pay rs.800 and that data pack will be valid for 3 months.
I said okay and they came to my working place and gave me new prepaid sim instead of changing the postpaid to prepaid. They activated the sim in dongle and i was able to use wifi with that sim and i paid rs.800 through debit card (I saw the vendor name is alai infocom). Also they told they will deactivate my postpaid sim.
But after few days the internet connection is very poor. Also my postpaid sim is not deactivated. I called customer care and requested to deactivate my postpaid sim also got to know no data pack is activated in my new prepaid sim. I got this info on 28th december.
I called to that number[protected] who sold me the prepaid sim. She told me, may be by mistake the pack didn’t get activated. She told me we cant give you the first time offer for that sim as its more than month.
So she told she can only activate this offer in new sim. I asked to refund my money. She told don't worry we will activate the offer in new sim.
Again she gave me new sim[protected] – balasundhari as per truecaller) and activated. This time i checked in my airtel app whether any pack activated. I could see rs.448 pack got activated. I checked in airtel website for any pack with rs.800 for first time users, i couldn’t find any. I called her again but she didn't picked up. Also today morning when i checked in my airtel app, no pack is active for my sim. How did this happen? I am calling her again and again from different number but no answer.
All were cheating?
How could the airtel provide my details to some third party that too there were many complaints. You can contact me through my email.