Data service signficantly decreased for the last week - can't use channel B66 anymore

We've been at our current location with T-Mobile for over 2 years and rely on the data service for internet service (we have almost no other options.)  In the last week, the service has really nose dived.  Speed is ¼ what it used to be, and worse is latency has skyrocketed. 

Before, I had set all devices to band lock to B2 and B66. This combination by far gave the best service.  When I checked the settings on our devices after it suddenly got much worse, I noticed it refuses to let any device use B66 anymore.  I normally have 2 and 66 set, but any device with those two set only use 2.  If I try to use just 66, I can't connect to the network.  With any device.  B66 suddenly not working has severely degraded service - is T-Mobile suddenly no longer allowing this channel?