I change my subscription from Pay per Traffic to Monthly. Then i try to back to default mode PPT but i see can’t change it any more and this is possible 1 per month. As i’m new to your service please change it back to Pay per Traffic.
Thanks
No problem. 
I’d changed your data plan to PPT (Pay Per Traffic) and reset your changable date too. If you’d like to change it back I think you can do again.