HSS send the cancel location to MME with cancellation type as subscription withdrawal to inform the MME or SGSN about the subscriber's subscription withdrawal.
This is what specs are saying -
The HSS will include a cancellation type of "Subscription Withdrawal" if the subscriber’s subscription is withdrawn by the operator and will include a cancellation type of "MME Update Procedure" if the UE moved to a new MME area and will include a cancellation type of "SGSN Update Procedure" if the UE moved to a new SGSN area, and will include a cancellation type of "Initial Attach Procedure" if the cancel location is initiated due to an Initial Attach from the UE.