Forceful recharge by Airtel for validity

I have a Airtel sim card and I am using it from past 7-8 years. I had recharged it with unlimited pack of ?448 for 82 days. But now today my pack has expired and they have sent message like if I am not recharging till tomorrow with unlimited pack they will deduct ?23 from my main balance to increase my outgoing validity. I have called their customer care executive at 10:30 am on Tuesday 25th Dec 2018, but without answering my query she disconnected my call. As a customer I think I will decide when to do recharge on my mobile. Airtel cannot forcefully deduct any amount from my balance without my permission. Request you to consider this case of forceful use of services by operator as there may be lakhs of consumers using that service and without their knowledge/permission if they are deducting amount then I think it is illegal.