HDFC Bank — one assist - unauthorized transaction

Address: Ajmer, Rajasthan, 305001

Website: www.oneassist.in

On 23-jan-18, hdfc credit card levied charges for an unauthorized transaction with the title 'one assist mfee' on 1399 inr. When i searched regarding the said charges then i realized that both hdfc and oneassist have been carrying out such activity on innocent users for more than a year.
Hdfc bank's helpline is not helpful as the phone never gets picked up. Similarly, the complaint redressal system never sends back any response.

I do not want the said subscription, and want a complete refund of the charges along with any frivolous penalty levied in this regard.