Misinformed About Voicemail recovery


My mom died. When my father switched us from AT&T to Verizon, the rep in the store told me that since I had an iPhone with visual voicemail that all of voice messages would remain even with the SIM change. That was not the case. they all disappeared.  They’re the only recordings of my mom’s voice talking to me that I have. I still have the old AT&T SIM card. Is it possible to plug in a SIM card to recover the voicemails just to save them to a third party device or cloud?

I feel I was purposely misinformed to make the transfer process quicker and I’m paying dearly.