I see the disappearing post syndrome strikes again......I answered this last night to the effect it looks like a ZTE model with a bespoke keypad.
If you take the battery out there should be a manufacturers sticker in there naming it as a ZTE product and giving the exact model number
As for "unknown brand" ZTE are in the same size league as HTC and Huawei. Massive. Relatively unknown as much of what they sell is through ODM/OEM badge engineered channels
(PS like Huawei there are similar concerns over ZTE's management's connections with the Chinese state security services)