AT&T has screwed me again by stopping my data before it has reached the 22 GB limit

I received a text from att saying I have already used 16GB and that att would slow down my phone if I used 22 GB however I won't ever reach the limit because I renew my plan in 9 days, BUT att did NOT wait and slowed my phone down when I haven't reached the 22 GB limit. WHY do they screw people out of their data usage when they just warned me that I was approximately 6GB away BUT I will be renewing it well before I can use that much data. But they didn't wait and wrongly slowed down my phone and it hasn't worked properly since I received the text from att. WHY? And they "conveniently" did it at almost 8 PM so I can't get a representative on the phone... they are closed.! What a rip!