SymptomsAfter removing subscription, the assignments to it remain in Lync Phone Numbers.
CauseAssignments are not deleted automatically when subscription is removed; provider has to remove it manually.
Open Lync Phone Number application and navigate to Assignments.
Click on the 'Show Search' link to expand filter settings:
Type the subscription id into the corresponding field and click on the 'Search' button.
Check the 'select all' checkbox and click on the 'Remove' link:
Click 'OK' in the appearing confirmation dialog.
All assignments will be removed.