You submitted a support ticket? You spoke with both a Riot representative and ensured it was not an issue with your computer? It would be one thing if this happened only the one time and you were placed in low priority queue, but something tells me this is either a persistent problem (in which case, you submit a support ticket and see if Riot's support team can help you. They are usually quite helpful) or you've afk'd before and Leaver Buster has already been tracking you.
I'll admit that Leaver Buster is kind of BS sometimes (people weren't loading into games properly and it would "catch" them, despite them having no malicious intent. I know people personally who have been "busted" even if they were reconnecting constantly due to computer/internet problems.....) However, in general if you encounter a problem like this for the first time, at worst you get a warning.