Staff damaged my item (Singapore)

An attendant and I got into a disagreement because I wanted to sit while the plane was boarding because there was a line and I have an injured knee. I sucked it up and stood in line. He began pacing back and forth and literally steps before entering the doors of the plane, the same attendant, who was also the one who stamped my boarding pass after security, approached us and said our carry-on item wasn’t allowed on due to lack of space. When I replied stating that he should have told us this forty minutes prior or as we were sitting in the waiting area, he backtracked and said “boxes aren’t allowed on the flight”. We told him to please handle it with care due to its fragility and he rushed us onto the plane. We had no time to take the appropriate measures to ensure its security as it was never intended to be checked baggage. Of course, we received our fragile sculpture back in pieces, with a tag on it that read "accepted at passenger's own risk". There was a space for a signature, which was obviously blank because we would not have signed it. As a result of this attendant's poor communication, and his neglectfulness, we lost hundreds of dollars on a piece of art that we will never get back. I have spoken to a customer service agent who after several followup emails, finally responded back saying there is nothing Jetstar can do. My fiancé and I are so appalled and will never be taking Jetstar again.

Vietnam-Ho Chi Minh City