If you want to disable old, pending communications in bulk, then you can do so through the Records Dashboard!
You will need to select "Communications" as the record type, and then select the status as "Pending"
We would also advise entering a "Created At" date, so that you don't accidentally disable any recent pending communications.
Once you have generated your list, you will see "Communication - Disable" in the Perform Action dropdown.
Select this, click "Action" and you will be all set!