T-Mobile Samsung S4 sees ATT network, but not T-Mobile

[captpete43]

properly functioning T-Mobile Samsung S4 stopped finding the T-Mobile network. Wor. It does connect with WiFi. When scanning for networks it would find ATT. Phone was reset to factory settings. This did not correct. A new SIM card was installed. This temporarily fixed issue, but it returned 1 day later.

HELP!