business saying that they've left voicemails

My dad requires a PCA and the agency that is in charge of maintaining the certification for the program is trying to say that they have been calling both my home and my sister with supposedly leaving voicemail which the call log and voicemails show that there have been no attempts and the voicemails only show one voicemail from a different individual about a month and a half ago.  before I assume that the place is lying is there anything that would cause there to be no calls/voicemails on my end from anywhere?