Angry [Q]pay at&t for tethering? not if I can help it!

Can anyone help me? Got an email yesterday from AT&T warning me to stop tethering (free), or else. My note 2 is rooted and running Scott's Rom's Clean Rom Ace 5.0. ? I was tethering with portable wi-fi hot spot app. Using about 8 gig per month.
My question is, since they have figured out that I have been tethering with this tethering app, should I have been using the hot spot toggle that is in the custom rom instead? Or would that make no difference. So, can anyone tell me if there is a way to continue to free tether without at&t finding out? I have a grandfathered in unlimited data plan and don't want to loose it. They tell me I have till the end of the month to stop tethering . If I dont, they will automatically enroll me in there fifty dollar for 5 gig plan. No way I'm going to let that happen. Any suggestions will be appreciated. Thanks.