Thanks so much for reaching out, sorry it's because you are hving coverage issues! Lets see what we can do.
Is this happening in a particular area, or are you finding it to be an issue all over the city? Are you using a T-Mobile branded iPhone? Is there anywhere you don't have this issue?
Just wanted to see if you've tried the steps above. Please give that link a shot and let us know if that helps. Thank you!