Citibank — Credit card agency black

Address:

New Delhi, Delhi, 110034

Hi i was using Citibank credit card. And as always had submitted an advance cheque in there drop box. I don't know how but they lost the cheque. I got a call from there end on next day of the due date. I paid the payment through neft. Thereafter i called as well as emailed the customer care ample of times regarding the matter but no resolution was taken out. Now they have made a bill of 15000 out of that late fee n interest on it. Moreover the company is just making misuse of cibil score n blackmailing for it on daily basis. Kindly help as it's just a mental torture for us and no regulations for the safety of basic consumer.