I recently received a 14 day suspension for abusive chat. I received two behavior warnings at the same time last week. I had no prior behavior warnings. Five days later my account is suspended even though i did nothing after i received the warnings. The chat log clearly shows that I was suspended for things i did before the warning was issued. I adhered to exactly what the warning said and was suspended any way.
If you are reported several times in World of Warcraft for violating the in-game rules, the game will send you a warning letting you know that you will need to be careful or you may get a silence or suspension in game. This is completely automated and cannot be seen or modified by Customer Support. If you receive one of these warnings, it is recommended that you make sure you are adhering to the In-Game Code of Conduct.
The automated system is not a replacement for reports that might result in a ticket. It is not a scripted and solid ladder that goes from warnings up to account actions. Just because you got a warning, does not mean there were not OTHER reports that were going to GMs.
What likely happened was that you were reported a bit ago, and it was in queue for review. You got reported some more in a way that triggered the auto warnings. Eventually the GM got to the reports, reviewed it, and determined if account action was appropriate.
Penalties these days start with around a week Silence, then move to Suspensions for further infractions. 14 days means that it was not your first account penalty.
If you want to know more about the policies you can ask on the WoW Customer Support forum. That is an Information Desk to get assistance navigating the support system and website, explaining policies, explaining shop services, etc. There are no GMs there, but during the work day usually a Blizzard staff member is around to answer questions.
If you want to appeal you would do so via ticket. Blizzard Support - Appealing a Silence, Suspension, or Ban
It also should be noted that even though you silence people for offenses you don’t allow them to make groups on any character, thus violating their game time and ability to play. Which has nothing to do with chat, since other people can invite them. Chat is one thing, but by making it harder to play their characters you are stealing their money and time. But we all know you won’t do anything about it.