Messages Being Blocked From Subscription Based Service

My company runs opt in sms campaigns for content creators online, and we have started to have a large portion of our ATT subscribers' messages blocked in the last day.

Can I get in contact with someone on your support team that will enable me to understand what caused the block (we have been operating without issue for over a month now) and how we can move forward quickly. We have a few thousand very upset users and we need to get to the bottom of this as soon as possible.