How do I stop data service while it's in use?

[Android Central Question]

T-Mobile Samsung Galaxy S9 -
I am experiencing horrible, horrible internet connectivity; so I do 'an network operator' search.
I choose "select automatically" to complete my search and receive a pop up message - it's "unable to search for providers while data services in use. Stop data service?"
I select yes and a message appears stating I'm "registered on the network".
Why is it happening?

 

[B. Diddy]

Welcome to Android Central! Searching for Network Operators won't help, because you're using T-Mobile. It won't help to look for another operator.

Are you sure you're in an area with good signal? Have you asked T-Mobile about your connectivity issues?