EXA technologies - Fraud agreement did by the company

Recently I got a call from Exa technology for a part-time job. They asked me to fill up ***** captchas within ** days with **% accuracy and on completion of job I will be given Rs *****. After this, they asked me to fill up a registration form by uploading photo and signature and Aadhar card. After filling up the form they send me a legal contract with my photo and signature at the bottom and a clause was attached to the contract which says failing to complete the work within the time period I would have to pay Rs ****/-.
Later I received a call from advocaterajivsingh**@gmail.com stating that I have to pay **,*** as I was late to pay the penalty of ****/- by * days. I was completely unaware of this clause and it was also not written in the agreement. He kept threatening me that legal action will be taken against me if I fail to pay the penalty. Please help me out of this problem. Quick action is expected from your side.