You're best bet is to fill a support ticket precisely describing your situation and be patient for a few days until it's solved, sometimes they make mistakes like that so maybe it's the case here.
Anyway usually hextech loot has nothing to do with afk, you usually just get low priority queue, but if you're often leaving games a punishment might be taken, which would explain your situation.
Did you received a low priority queue ? What was exactly this message about ? Because if it's a punishment ( you drop in honor and loose hextech loots ) then it's totally normal.
If it's really a mistake from riot and you havn't been punished they'll fix it.