Builder not returning booking fees of 5lacs after cancellation

We have booked 5lacs for Vasudha Green Apartment near Kamalgazi , Kolkata on 8th September 2019. The agreement was done between us and Senco Infrastrucure Pvt Ltd. But due to some financial problem, we decided not to buy this flat and submitted Cancellation Application on 15th September 2019 to refund our money back. The cancel application was received by their employees Aparna and Diponkar Dhar (with whom the initial agreement was done). And they told me that the money will be refunded by the end of October. Also, as per the agreement paper (booking application form), the money should be returned back within 45 days. Now it's over 65days and still, I didn't receive my refund money nor getting a confirm date of refund. And they are not giving any dates to return the money?? Kindly note agreement was done on the builder company application form and the amount was paid to the company via Cheque. How can I get back my money?? Also how long it could take if I have to file a lawsuit against the builder company?? Regards Kuntal