You can easily cancel or release the numbers that you purchased using IMIconnect but do not use any longer. If the number is currently in use or is mapped with any service, you will need to delink it before initiating the release.
Once released, the number is made available for use to other users. You may not be able to acquire the same number again in case somebody else buys it.
Numbers are billed on a monthly rental basis. You will need to pay the rental charges for the whole month even if you release the number in the middle of a billing cycle.
Steps for releasing a number:
Login to IMIconnect and visit 'Numbers' section
Click on the 'Manage' button against the phone number you want to release
You can see the phone number along with subscription details. Click the 'Release Number' button to delete/cancel it
If the number is mapped with any service, you will get the following message and will need to delink it first.