Being Harassed for Credit card bill even when card has not been used

I have taken a credit card of HDFC Bank in Aug 2015. Due to some reasons I was not able to activate it or use it till date. I started getting calls from HDFC for various things and ads continuously. I got calls for HDFC insurance departments as well in which they asked for details like date of birth , card details etc.At that time I was not aware that HDFC Bank and HDFC Ergo are different. After few days of that call I started getting payment mails of Rs. 13000 for HDFC Ergo. The payment amount kept on increasing and even a legal letter was sent to my home stating I have not paid bill for HDFC. This is causing me mental and social harassment. I have even been trying to contact HDFC Grievance cell since then and I have not been getting any response. I have concern that my credit score will be ruined if this issue is not resolved, I would suggest no one to deal with HDFC Bank as they have caused me so much trouble. I want to file a complaint against this in Consumer Forum and need guidance on this case.