Voicemail PIN Not Working on Desk Phone

The Voicemail PIN is not working on a couple users' desk phones. They are on Polycom VVX450 devices. The PIN has been tested immediately after changing it, a couple hours after, and a day later and there's still no access to voicemails. They can still be checked on the computer app, but some users are not utilizing the computer app and require access through desk phones.

Phones have been rebooted after the PIN change to no avail.

Any advice?