Yeah, I had this problem and it was a total pain! But I solved it by simply installing Squid Cache Proxy server on my physical PC, and that way my host-only internet virtualbox PCs could connect to the internet!
I did a quick 3 minute guide here - for anyone who wants to how it works!
This involves installing open-source proxy server on your PC – once done, your VirtualBox ‘Host Only’ Guests can connect to the internet via your computer.
Step 1 > Install Squid-Cache for Windows – click here for link
Step 2 > Allow Port 3128 on your PC’s Firewall