The K3772-z often acts as a CD-ROM (virtual drive) first. You need to switch it to "Serial/Modem mode."
: Travelers can insert local SIM cards while abroad to avoid expensive international roaming charges from their home provider. Device Longevity UNLOCK K3772 z VODAFONE USB MODEM
Sometimes you can bypass the lock by creating a manual Windows dial-up connection. : Put your new provider's SIM into the modem. The K3772-z often acts as a CD-ROM (virtual drive) first
Have you successfully unlocked your K3772-z? Let us know which carrier you switched to in the comments below. UNLOCK K3772 z VODAFONE USB MODEM
What (Windows 10, Mac, etc.) are you using? Dongle Unlock Code | PDF | Modem - Scribd