Theres no way to ever avoid hackers in games, but the best choice of action to deal with them is to just keep trying without accusing them of hacking. One of many possibilities can play out when you accuse someone of hacking, the first being they say "Nah im not hacking, you just suck" which will get you mad. The second being they start to hack less, trying to make it unnoticed by overwatch.
My choice is just to simply mute them in-game and continue playing trying your hardest, if the player is hacking he will get reported and banned eventually. I dont remember for sure, but I believe if the person you were against was hacking gets vac/overwatched banned you will receive a win for that match instead of a loss.
Just remember to have fun with comp games and kick everyones butts instead of focusing on if someone is hacking or not, chances are they may be smurfing or just really good. You wont get a perfectly even match every time.