Note the packaging from Oracle's site is rather different (and probably incompatible), as everything is included in one package. You are probably better of purging all virtualbox-* packages before moving from one to the other.

dpkg --purge virtualbox virtualbox-dkms virtualbox-qt

(and any others I didn't include)

Wrong command. Assuming you want to install the version with your OS (distributed as separate packages), You wanted:

dpkg --configure  virtualbox-dkms

dpkg-reconfigure is intended to re-ask debconf questions, not to fix broken packages.