Your source seems to relate only to ATC transcripts but with the radio silent on the ground from the Legacy does not mean that attempts were not being made in the air from the Legacy.
My source is the NTSB. You can go and look their site:
www.ntsb.gov. The pilots confirmed this report. They did not try to contact Cyndacata in Brasilia before the attempts described in the NTSB report. They said that the radio was working fine because they would hear Cyndacta talking with other planes. I did not know why later they tried to contact Brasilia so many times, neither I read anywhere why they tried so hard at that
particular time. I am not sure if it was to discuss altitude. They did not understood the new frequency they were given for Manaus.