Help 4G not working properly

[Android Question]

I recently purchased a S6 on straight talk and for about 5 days my LTE was working fine then all of a sudden it went to 3g and will not return back to LTE I've tried everything.... please help

 

[Hadron]

To avoid repetition of stuff you've already tried it would help if you told us what you have done.

Obvious one: have you spoken to your carrier to make sure it's not a problem at their end (including an error in your account settings)? Have you tried your SIM in another phone to see whether you can get LTE that way (which would either identify or exclude the phone itself as the location of the problem)?