Unlocked T-Mobile S7 phone not getting LTE
I recently purchased an unlocked Samsung Galaxy S7, which was unlocked from the T-Mobile network. I took it in to my local store and they added the nano SIM and such. The phone worked great except I didn't get LTE and my voicemail wouldn't work. I chatted in and we got the voicemail fixed, but I'm still unable to get LTE. The chat rep said that my phone might just not get LTE.
I had an S3 previously, which had LTE basically everywhere. I did a Speedtest.net check with my new S7, compared to my boyfriend's old S3, and he gets better speeds than I do. The only difference is that my phone is newer and my phone is an unlocked T-Mobile phone.
I have read online that this may be something to do with "HSPA" being my mobile type, compared to "HSPA+." When I asked the chat rep, he didn't really acknowledge this.
Does anyone have any experience with unlocked T-Mobile S7s being used on the AT&T network? Is it normal for me to not have LTE when I had it previously with my old phone in the exact same place, and the people around me have LTE? Do you have any suggestions about settings I can change or things I can do to somehow fix this, beyond buying an AT&T branded phone to replace it with (not an option)?