Can't WiFi tether on AT&T plan that allows it..

I am using my SIM from an iphone, and my stock device won't let me enable WiFi hotspot, telling me it needs to be enabled on my plan. The tethering worked fine on the iphone and the 3GB Mobile Share plan I am on says that it is permitted.

Do other people have this working? Is this because they don't have my proper IMEI attached to the SIM? Does AT&T have these IMEI numbers in their database or will I lose LTE if I update my IMEI?

Completely wiped my phone, can't get stock ROM unto it...

I wiped the internal storage on my phone by mistake and now my phone has no OS or ROM to flash it back on. I tried to sideload with TWRP but the feature wouldn't start. I flashed the stock recovery and tried to sideload it there but I get an "error: protocol fault (no status)"... I tried to mount storage on TWRP but that feature didn't seem to work on it either. It's a good thing that I still have my OnePlus One to use, but I would appreciate your help!!

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