Singapore Airlines — check in

I was travelling from Singapore to Perth WA on flight SQ 0215 on 21st January 2020 with my daughter. We arrived 2.5 hours beforehand to be checked in and do some duty free shopping and have a massage. At the checkout we were asked if we were interested in being upgraded to business class and have a hotel and meals paid for, or $400 cash each, if we flew in the morning, as our flight had been overbooked. I accepted the offer and said i would be happy with either the cash or the upgrade. We were asked to wait nearby while this was arranged. After waiting for half an hour I inquired with the check in clerk when we would recieve our new booking. He sent me to the information counter to talk to another Singapore Airlines staff member. The woman at the counter told us that they no longer needed us to change flights and that we could check in again. She offerred us a meal voucher of $15 each as compensation. She was very rude to us. We were then given seperate seats on the plane and had to wait to see if they could ask another passenger to swap seats so that I could sit with my daughter. This was done just before boarding. My complaint is that we were left to wait with no information about our booking, we missed doing any duty free shopping, or massage. We didnt even have time to use our meal voucher as we had to head straight to the gate after all this time waiting. We were deeply disappointed that we had been offerred the upgrade and had it reneged. We felt used by Singapore Airlines to have us wait in case they needed us to help them out, and when we were not needed they stuck is in terrible seats without an apology. In fact the information staff person was very rude, and got terse with me when i complained. I feel that Singapore airlines should aplologise for doing this to us and make restitution for the way we were treated.