It looks like Palmstore is Itel's preloaded app store. Do you ever use it at all, or do you use a different app store?
If you never use it, did you go to Settings>Apps, select Palmstore, and see if there's a Disable button there? Or is that what you mean when you said you "deactivated" it? ("Deactivation" is not the typical term used in this situation, which is why I'm trying to clarify.)
The next time that notification appears, see if you can long-press it before it disappears, and then tap the settings icon that shows up to adjust the notification settings for whatever app is responsible. (There's a slight chance it's not the Palmstore app, but something else that was preinstalled in the system.)