SMS sending is auto-blocked, how to fix? To a specific number, when I try to send a SMS, it is automatically/instantly blocked and fails.

Once, by mistake, I blocked sending messages to that number, but even after unblocking, the messages are still being blocked as if that number is still blocked.

I have deleted all old messages to that number, and also deleted all data and cache of the Messages app.



I have also tried to block and unblock again.
I went to application settings for this app but all looks ok.  

I can send SMS to other numbers, it shows a waiting spinning icon and sends properly. But for the problematic number, it fails instantly, as if it doesnt even try to send the SMS at all, is blocked locally, by the Messages app...

Galaxy J7 Marshmallow.
I didnt find a fix the bundled messages app.
As workaround I just installed google's one and after 2 years I can send messages to the specific number again, thx!