This worked for me:

 #!/usr/bin/env bash

 url='https://www.vpnbook.com/freevpn'
 html=$( curl -# -L "${url}" 2> '/dev/null' )

 username=$(
 <<< "${html}" \
 grep -P -o -e '(?<=<li>Username: <strong>)(.*?)(?=<\/strong><\/li>)' |
 head -n 1
 )

 password=$(
 <<< "${html}" \
 grep -P -o -e '(?<=<li>Password: <strong>)(.*?)(?=<\/strong><\/li>)' |
 head -n 1
 )

 printf '%s\n' "Username: ${username}" "Password: ${password}"