This is...Unusual, to say the least, but, if you feel you deserve a higher tier of punishment or that a lower tier of punishment was incorrectly applied, you can submit a Support Ticket to ask for the proper punishment tier to be applied.
I have heard that the Gameplay and Chat-related behavioral tracks are generally kept separate, so, it may be worth specifying to Riot that you don't simply want the punishment stepped up a tier, but that (provided you still flamed in that match) you be bumped up in the Gameplay punishment track.
Either way, I hope this information helps.