How to deal with people getting help on board We all had this situation where our opponent have this fide master friend and just happen to stand next to him, whisper him things while pointing your chessboard.

I've never had the guts to call it out (that would make a mess out of no proof accusations) but that usually mess up my game as my anger take over my concentration.

I'd like to know if you've met this situation and how you dealt with it, or what would be the official way to deal with it.

Please consider that calling out referee might not be the best solution : as I said, there's no proof, and it's easier said than done to call a cheat when there's no evidences.
What you describe has never happened to me personally, but I would have no qualms of making a complaint in this situation - either by calling the arbiter (in the case of a tournament) or my captain (in the case of a league match). What you describe is clearly unacceptable conduct in any rated game.

To illustrate how little is needed for an issue to be taken seriously: I once played a kid of about 6 years old - he was a good player (on my level at least), but he struggled to write down the moves properly. His dad came over and started to correct some of his notation. My team captain immediately complained to his team captain, and the dad was asked to leave the playing area. The question of proof was not on the table - just the fact that one person may be uncomfortable about something is enough for a referee to impose strict playing conditions even if no misconduct actually occurred.