International SIM cards not working in my unlocked S7

[StankinJankin]

Hey everybody! I'll try to be as specific as possible here. This is my first time posting, though I've been peeking here plenty of times for quick fixes.

I'm travelling around the world without flying, which should take me quite a year or two. I've been planning this trip for years, and chose this phone specifically for it.

I bought a Samsung Galaxy S7 SM-G930T 32GB 4G LTE GSM Black Gold T-MOBILE on Ebay in March 2017. I had been using T-Mobile for years prior with an S4. I connected this S7 when I received it, and it's been awesome. I immediately informed T-Mobile of my long term plans, and they said I would have to wait ninety days after requesting an unlock until I could unlock it. Ninety days later, They sent me a link to a T-Mobile app called Device Unlock. I had a choice of Permanent or Temporary. I chose Permanent, got the confirmation that it was permanently unlocked (no turning back), and then I called T-Mobile to disconnect my service.

Three months later, after happily using the phone only to connect to wifi, I arrived in Japan. I went to a Bic Camera to buy a SIM card. They're awesome, so they allow you to try before you buy. It doesn't work though. There is no error message, or anything like that. It just doesn't work. The employees at the store are calling each of their co-workers over to look at it, and they're all perplexed. There is a whole section of the store dedicated to travel SIM cards and tourists buying SIM cards. These employees are doing this all day, every day on phone after phone, but my S7 is the anomaly that they all scratch their heads at. The SIM card works fine in my girlfriend's Galaxy S6 Edge Plus.

I hoped it was only a Japan thing, so I was patient, but now I've had the exact same experience in China (I found plenty of wifi in South Korea). The employees in the store do not understand why my phone will not work the way that every other phone does, but my girlfriend's works fine.

More specifically: After the SIM card is inserted and the phone is restarted, for about a second it will show the signal bar full as it should in the upper right , then it goes back to empty with a little X. It seems as if it's capable of recognizing it, but only for a second.

Multiple employees at multiple stores in Japan with multiple SIM cards checked the APN settings, and the employees at the one store in China did also. Everything seems to be correct.

Sorry for the super long post. I read the "read this first" post and was told to be as specific as possible. Only other thing to note is that my phone was sold to me as a 32GB phone, and it is in fact a 32GB phone. However, when entering the IMEI number into a free IMEI checker, it shows 64GB. Could this be a factor?

Thank you in advance, and I'm sorry for the long one.

 

[Rukbat]

First, the "permanent" unlocking is something you don't have to "go back" from. That just allows SIMs that aren't T-Mobile to work in the phone. (Otherwise you'd get a request for the unlock code.) When you get back, if you put a T-Mobile SIM in the phone, it will work as always.

Second, I'm as perplexed as the store employees in Japan and China. The phone has quad band 2G, so you should get at least voice and text. (The frequencies in the phone are 700/800/850/1700/1800/1900/2100/2600 [Bands 1,2,3,4,5,7,12,13,20], so you need a carrier using bands that the phone can handle for 4G.) But voice and text should just work. (Maybe, when you were in South Korea, you should have brought the phone into Samsung and asked them what's wrong with it.)