Mobikwik — Zip Bill

I never applied for zip bill but one day I am going to recharge my mobile through my debit card from Mobikwik but when we click on recharge the recharge done automatically. I was confused that how recharge got successfully without giving debit card number but after one month I am receiving message from mobikwik that your zip bill is created for Rs 654 something (Don't know the exact amount right now) and receiving call also. I told to executive that I never opt for zip bill and I wanted to recharge my mobile through my debit card but recharge done automatically. I can pay Rs 555 the recharge amount but i will not pay the extra money. But they are torturing me and sending me many messages regarding bills. They do automated calls many times in a day. Now they are increasing my bill to 954/- and threatening me for further penalty. They are mentally torturing me though I am ready to pay Rs 555 the actual recharge amount. Please Help