I have faced the same problem twice - once each in Airtel-Karnataka and Airtel-Goa. Complaint: I ask an Airtel agent for a top-up/recharge, and instead I end up with a plan change. So instead of getting Rs188 talktime recharge, I end up with a Rs1 talktime and a new, 'bad' plan. So I lose money at the time of recharge, and on an ongoing basis because the new plan has very poor facilities.
And after that it is impossible to explain the problem to Aitel customer service and get the problem rectified.

Phone number where the plan changed: 9975569921