omg! im having the same issue too! with Verizon!
i recently went to israel and was using an israeli sim card. when i came back to america, i put my verizon sim back into my iphone 7 plus ( with ios 11.0.3). the calling and texting was working but not the DATA at all!!!!! was soooo frustrating! i spoke to verizon for hours on the phone! and they transferred me to apple. i tried everything (restarting phone, reset network settings, reset all setting, taking out the sim etc.) they finally said we have to back up the phone to a computer and restore it. we did that! so frustrating because now i must sign back in to all my apps! anyway IT DIDNT HELP!!!! so the next day i went to a verizon store ( maybe the im was physically damaged.) they gave me a new one, and the calling and texting worked, NOT DATA! they tried hta sim in another phone and LTE worked totally fine!
verizon said it must be an apple issue, so i scheduled an apple appointment ( besides the fact i waited 3 hours in the store!!!)
i called my aunt as i was waiting ( she's good with phones and tech). she said go to SETTINGS>CELLULAR>CELLULAR DATA OPTIONS>ENABLE LTE> OFF to try to see, wait a bit and go back to VOICE AND DATA. i waited and a 3G icon showed up at the top of my phone. all of a sudden messages from whatsapp (data was working) were coming in! but only at 3G.
i tried going back to VOICE AND DATA but then the internet would stop. so i just only used 3G.
then i went to the apple store and they said since you're still on warranty well give you a replacement. they did.
last night i updated the phone and restored it and still have the same issue!!!!!! my LTE WONT WORK!!!!!!!!!!!!!!!!
HELP MEEE