Hi
When does your billing cycle start? Do you have an LTE phone? As far as I understand, your speed can get reduced if it's projecting your usage to be much higher than 5GB (LTE) or 3GB (3G) for the billing cycle, for example if you used 50% of your plan in only few days. If you have any account specific questions, you can send us a private message by clicking here.
Thank you,
Dmitriy