If they're on your friends list - then the setting in WoT's General settings wouldn't matter, since it only toggles on/off getting invites from people NOT your friends.
Not sure if there's a mod that can be setup to block invitations... might be an idea to attach log files.
How to:
Run the special application called "Aslains_WoT_Logs_Archiver.exe," which can be found in the game installation folder or as a shortcut on your Windows desktop. This application will create an "Aslains_WoT_Logs.zip" file. It is mandatory to attach this file to your thread. Please note that I don't need any other logs, only the specific zip file generated by the "Aslains_WoT_Logs_Archiver.exe." You can find the "Aslains_WoT_Logs.zip" file in the game folder inside the "Aslains_Modpack" directory.