Why wont my unlocked HTC One M9 get 4gLTE?

[Android Central Question]

I use the carrier straight talk, and I purchased an AT&T sim card. I spoke to customer service for over two hours and messed with the APN settings like they told me to do..
I can send texts and calls and I can use limited data.. but it shows an H instead of 4g like I paid for.
I bought a 55$ plan from straight talk to activate the phone... and now I'm barely able to use it.
Is there any way to get 4g or am I stuck with whatever this H is?

 

[B. Diddy]

Welcome to Android Central! If you have the European variant, that doesn't support any of AT&T's LTE bands:

https://www.gsmarena.com/htc_one_m9-6891.php#europe
https://www.frequencycheck.com/carriers/at-t-united-states

So if that's the case, you're stuck with 3G (H stands for HSPA).