Hi.
I downloaded the ROM "black view-bv8000 pro_2018062921_s21v57c2k_jk_tee-ota" from your forum and I used the Local Update's method and did a Factory Reset but the phone was still in Android 7.0 when i finished to install the ROM. What should I do ?

You'll have to flash your device to a previous android 7 ROM (20171219 or 20171227), and then try again to perform a local update to Oreo.
All is written here!
viewtopic.php?f=192&t=436084

Hi

I´m in the Brazil using bv8000 pro android 7. Here the smartphones already have  android 9 . Is not fair with us to wait long time by update android 8 and with many probs.
Many people here don´t want do a local update !!!.
We have hurry this OTA update. I think about having the android 9.
Buy we and want attention !!!

tks

Yeah mate, good luck with that. As far as BV is concerned, this phone is dead.
They won't support it anymore (it lasted what, a year ?) because they're too busy selling a shit ton of "brand new amazing phones".
Their business model just doesn't leave room for software update.