The Receipt Message is an automated text message that is sent to your first time missed calls. It's located on your 'Account' settings page on the left menu:
This Receipt Message sends to the First Time Caller the following:
Any text included on your "Receipt Message" text box. If you wish to edit the Call Receipt message, you can simply edit that text field.
A webpage link for the caller to access details about their call, like the date and time, and keep for their records.
Here is an example of the message sent to the callers:
If you want to completely disable this feature, just set the 'Receipt Frequency' to Never:
Then hit Save at the top right corner.