Solitaire Technology Company — About the form filling work from home job

I am a graduate looking for a home-based job during this lockdown. I have applied for work from home job on the quikr website then on 5 Jan 2021 a person contacted me and told me about the form-filling job without any investment and then I applied for the on and started to work. I was working for 15 days and submitted my work before the end date that is 15.01.2021. I submitted the work but on 18.01.2021a person called and told me that I have not submitted the job. So due to the incomplete job work, she is telling me to pay the penalty money and threatening me that they will take legal action against me, and sending me the mail with the legal notice. What should I do but sure I have submitted my work.