Ds Services — fraud legal matter

I wanted to earn money so i searched some freelancing jobs. I found a job on quicker named as ds services that i felt could be genuine. They forced to sign me a virtual legs contract to start work. They took my address proof and gave me the work of form filling of 1500 pages in 10 days. I completed the work on time and also checked the work twice because the money was to be deducted for every wrong page. So i submitted the correct work on the given time. Two days later they send me a mail saying you didn't submitted the work on time so you have to pay 7510 as utility and they also imposed false allegation that i abused the client. They said if i don't pay it then i will have to pay 50000. When i called them and said i submitted the work they immediately send me a report showing that my work failed. They are now threatening me every day on calls and sms that they will send me legal notice and will take legal actions on me.
I am very much depressed and stressed due to all this scenario.

If anybody is going through the same problem please tell me how to get rid of this.
Pls
You can mail me at : [protected]@gmail.com