SriLankan Airlines - Flights cancelled and Not refunded

We booked flights from Chennai to Singapore in Srilankan Airlines. After check-in and clearing immigration, we were told that the flight is rescheduled and the connecting flight in colombo is also cancelled. As the passengers are ladies and we had immigration appointment in Singapore the next day, the airline staff advised to offboard.
We also offboarded and booked alternate flight to Singapore.
The Srilankan airline advertised promotional fares but it seems that they are cancelling the flights and not returning the money.

Due to this we have paid * times more than the usual fare. After repeated tries also, we were unable to get the refund.