Airtel — poor services, worst commitment level of customer care reps.

I carry an airtel postpaid connection with mobile number [protected] for many years now.
Lately due to poor service i wished to port out from airtel thus requested for port out code, the retention's dept rep. offered infinity plan of 349 with unlimited calling and 31GB 4G data/month. since that very moment my data has completely stopped. i called customer care multiple times but every time they tell me some diagnosis steps. I'm perpetually trying to explain that it stopped after plan change prior to that it was all good.
The supervisor on floor named shikha tells me that my handset device has gone faulty coz everything is good in airtel network. she is unable to give me any logic behind how was data smoothly working before plan change and how can suddenly phone can go wrong. she ended up being rude on call and denied to help further.

I demand my plan benefits and why should i pay for services that i'm unable to use.