Is there an official otg usb cable for the BV9700 pro?
Is there a possibility to know where to buy one with the right size? 
10mm right?

Recently a malware has been discovered in many apps of the playstore among these there is also the app "compass" is this installed by default in the phone?
Link info: https://www.generation-nt.com/android-2-malwares-12-applications-playstore-actualite-1973558.html

Personally I prefer a solid and powerful phone like these from blackview instead of very up-to-date brand models but that, if you fall once by half a meter you can throw it in the trash. The price of the hardware is affordable compared to samsung, sony, etc ... performance has nothing to envy to bra...