I thought so too but then I realized that it’s been five years since he heard her voice ykwim so I kinda get why he couldn’t recognize her
Spoiler! Spoiler! Spoiler!
.
.
.
.
.
.
.
.
.
.
.
.
.
It's not that he doesn't recognize her voice, he actually does. In the later chapters we find out that he was scammed multiple times by people claiming to be Paula and having the same voice as hers. So he doesn't trust anyone anymore, that's why he was so reluctant to believe that "Anne" was Paula. Also by the storytime about the dragon he figured it out, but reasoned that she wanted a secret for whatever reason!
I cant understand how he cant recognise her voice you became attached to this person when you were blind you surely know thier voice thier touch . At this point its just stupid that he cant recognise her