Unable to connect to world

Good day, 

I would like to submit this letter to ask for an immediate fix or solution with this problem. We've been playing minecraft for a month or two and yesterday we have encountered an error message "Unable to connect to world" whenever I try to join my friends' world and vice versa. May I request for a possible solution by the way we tried restarting the game, uninstalling and reinstall it , well almost everything but nothing works. Hoping you can help us.