Assistance needed for network problem!! Samsung T-589!

Hey everyone, and thanks for taking the time to read this in advanced.

I recently got a t-mobile T589 Samsung gravity smart before going on a lengthy trip to Japan.
I immediately unlocked the phone as soon as I could, and placed my SoftBank sim card inside. It worked, but my problem now is my Samsung wot even search for the network!!!

Everytime I go into my wireless settings and try to search for the network, it just searches indefininitely. And if I try and switch the search from automatic to Manual, it either searches forever again or kicks me out of the mobile network menu all together! I even tried to find the network with my T-Mobile simcard(because with my previous phone I could at least connect to softbank and be roaming) and it still refused to search.

There is also a circle with a line through it next to The battery level icon that I've never seen before.

Any kind of insight or advice would help!! Thank you again for reading

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does no one have any suggestions?? I'll try anything please!!