I was the one who posted earlier about the ,hipri fixing my data connection, sorry this hasn't worked for you. What else have you tried? I would start with a battery pull, let it sit for a bit and then restart, just to make sure. If that doesn't work you could always try a non LTE APN to see what happens. If you can connect to regular data but not LTE, that might tell you something. I will attach a screenshot of the settings, add it as an additional APN, don't replace the LTE one. If this still doesn't work, I would try a new sim card from at&t just to be sure. Last resort to me would be a factory reset or exchange the phone entirely.