Oklute.com — Service had received money and not providing service

I have found a service provider from your website we both agreed on an amount of 300rs i have payed my fees now they are saying they will need a aditional 1250rs when I am telling to refund my 300rs they are not refunding please do something for my situation otherwise i will have to file a complaint against your website
Thank you
Yours sincerely
Prem