T-Mobile blocking websites?

I've been unable to access my Comcast e-mail for the last few days when I'm on the T-Mobile 5g network.  I keep getting a message that there is a log in error due to a temporarily blacklisted IP address.  I have no problem accessing my email when I'm on my home wi-fi or any other wi-fi network, for that matter.  Xfinity said it wasn't their problem because it works while on wi-fi.  T-Mobile customer service was very nice, but couldn't help me.   Any suggestions?