You could possibly use the Google Contacts "Import" feature to create a single contact listing all 10000 phone numbers that share that 6-digit prefix. There might be a phone number limit, if so try making 10 contacts with 1000 numbers each (or 100 with 100) - then group them and block the group.
You can see the correct format for a contact with multiple ...
"The only workaround for this is to use Google Voice's call screening function. When you turn on call screening, GV will require whoever or whatever answers a forwarded call to press 1 to accept the call." Google forums
Web Skype can not call phones until you install a special plugin.
The plugin download will be shown when opening web Skype if your web browser supports it. Unfortunately it does not support ChromeOS, Linux, WinRT, and only supports a few specific browsers on Windows and Mac.
After installing that plugin, a "Call phones" button appears on web Skype: