How do I contact Tiger Airways?

Tiger Airways has changed the timing of the flight I had booked from Singapore to Bangkok, and sent me an email saying they will rebook my flight on another day at no extra cost. For this I am supposed to contact their telephone number. But I find that it is almost perpetually engaged. When I have got through with great difficulty, I have been kept on hold for more than half an hour without any reply. How can I handle this?