Link Star - Harassing me to pay money for cancelled registration

Linkstar form filling has contacted me for form filling but the agreement was not explained properly that I have to pay **** rupees. I have cancelled the registration immediately after the registration itself to the mail I have received where credentials were sent. Even I called customer care people, they said to me to reply to the same mail having credentials that I want to cancel my registration. I replied the same to the mail on that day itself. I even have mail proof also. From that day onwards Linkstar people have started harassing me for every call, I informed the same. Now they are calling again and saying we will take legal action which is fraud behaviour against the consumer.