Some people are saying "Maybe you are more offensive than you think you are." They are correct. However:
It is possible to be 100% silent in games and receive "Your language was offensive" notifications. This happens to me frequently. Again, I am 100% silent in games.
Regardless of whether the OP is toxic or not (we have no way of knowing), it is true that the report system is very flawed, and it is common for the losing team to report each other, regardless of whether or not those reports have merit.
Getting reported consistently is NOT ALWAYS a sign of toxic behavior. A string of losses, trying out a new champion for a few games, or just having bad luck finding friendly Solo Q teammates multiple games in a row can lead to consistent report.
Lyte has said the most common word toxic players use in chat is "report" - a sure sign that the reporting system needs to be changed to discourage the truly toxic players from using it as a tool for revenge.