Iv'e had the same thing happen to me but i knowingly bought a t mobile lg v20 for 20$ in mint condition. A buddy had a t mobile plan and he lost his job and couldn't keep up with his bills so his act went in the rears. So i bought the phone not really knowing it was blacklisted and i didn't really care it's not my bill and how could i really lose it was on H91810j firmware so root and recovery was possible so therefore it is modded with a custom rom, twrp recovery, xposed is active, working great. So i tried a IMEI changer and used my clean and clear t mobile lg v20 IMEI # and it's still blocked from activation on t.mobiles network , but you look in the phones gen settings in IMEI and it's listing the new clean IMEI so with that being said there seeing the phone from some other info besides the IMEI. So i'm thinking of having it unlocked and using it on AT&T ( straight talk ) pre paid act. Mind you i don't really care if i get it working but it would be nice. Any ideas or suggestions or info from personal experiences and do you think having it unlocked will work on AT&T i know they share the blacklist datbase.