Stop payment of cheque

Hello Everyone, I want to start a online business, and for that I contacted an IT company for create a website and an application. Company provided me quotation on my mail, and asked me to deposit 50% of quoted money to companies account, and promised to deliver that product in 45 days. I deposit 20% Rs 20000 of total amount in company's account and asked them that I will pay when work will start. Now that company denying to work on this project and not delivered that application and website after 45 days of initial payment. I asked to refund, initially they promised to refund within 7 days, after that they delayed for another week. (mentioned on whatsapp) Now they gave 10% of payment via post dated cheque, and stopped payment on that CHEQUE, and challenging me that they will not refund money over the phone. What can I do now?