Why do I get this Uber message ““we can’t reach our network right now” ?

Often when I try and user the Uber application for a ride I can’t complete the ride request because I get a message from Uber stating “we can’t reach our network right now”

We use T-Mobil on our new Apple I-phone.

We use the I-phone only for telephone calls and to use Uber for our rides.

Recently we switched from T-Mobile $2.00 a day when we use our phone or use Uber, to a T-Mobile $20 per month usage.

Is the problem with the new T-Mobile monthly charge.

Why do I get this message ““we can’t reach our network right now”

Thanks for your help,