Any account (active/disabled) which has a phone number rented, will incur the monthly charges, although the number is not being used. Only the usage charges will not be added as the number is not being used. However, if you have closed your account (can be done from console), all numbers associated with that account will be released and the account will be deleted or closed.
Accounts that are inactive due to pending verification or suspension due to detection of fraudulent activity, will incur phone number rental fees for phone numbers associated with that account as the numbers are still in the account.
In case, you wish to close your Plivo account, you can do it from Console. Please refer to this article for details.
In case of any any queries, do contact our support team for assistance: https://support.plivo.com/support/home