In Settings -> Blocked Destinations, you can add numbers to a blacklist, and these numbers will not receive messages from TextPeak.
To add phone numbers to a list of blocked destinations:
Prepare a CSV file with numbers to block.
On the Blocked Destinations tab, click the Add Blocked Destinations button.
On the page that opens, upload the CSV file you have prepared and click Next.
Select the file column that contains phone numbers.
Select the checkbox under the table if the first line of your file contains column titles and you want the program to ignore it.
Click Import List.
You will see the summary of your file in a pop-up window. Review it and click Confirm.
The list will be added to the table. By hovering over the progress bar, you can see how many contacts have been parsed successfully.
If you want to view the blocked numbers, switch to the Phone numbers tab above the table.