Login to your Google Voice Inbox, click on settings>voice settings in the upper left corner, and then click on voicemail & text. That is where you control whether you're notified or not. Is that what you meant?
You're getting a notification that you got a notifications for your notifications!
Hehe
I hate to ask this question, but you did click the save changes button after you made the changes on the website, right? If you unchecked the checkboxes for Voicemail notifications and text forwarding, you shouldn't be getting those.