Cancelled flight in April 2015

I booked a flight back in Decmeber on the morning flight, departing 29thApril. This is the best flight time as you arrive in Bali around lunchtime. In January, Jetstar cancelled this flight and sent me an email, my option was to go on a later flight. I found out that there is an early flight two days earlier, so I called Jetstar and got put through to an call centre outside Australia. I explained that I was originally on an early flight and the flight was cancelled by Jetstar, according to the call centre staff it was cancelled due to safety issues. I would like to know how they can identify a safety issue 3 months in advance?..She did not answer the question. I asked to be moved to the early flight leaving two days earlier as we had booked a two day excursion on our arrival and the new flight would mean we have to cancel as we arrive too late. If we left two days earlier the tour guide would move our booking, just needed Jetstar to move flights. It seemed a fair request, but once again rather than provide customer service, they stuck to the T&Cs and said it would cost over $600 to change flights.

I really would like to know how you can change a flight that is 3 months away due to safety issues. What has happened to customer service, and why they can't be reasonable. Come on Jetstar, you are a company providing a tourist service, yet you don't how to service your customers.