http://www.pcgamer.com/overwatch-competitive-permabans-are-coming-next-week/

Blizzard has issued a warning to the Overwatch community that beginning next week, players who have accumulated three or more seasonal bans will face a possible permanent ban from Competitive play. And permanent means permanent: "Neither seasonal bans nor permanent Competitive Play bans will decay or reset over time," community manager Josh Engen wrote. "Once an account is permanently banned, it currently cannot return to good standing." 

"Starting Wednesday, September 27, any player who accumulates three or more seasonal bans may be permanently banned from Competitive Play, removing their ability to participate in any future matches in that mode," Engen wrote.