Impossible to connect my "Go color 7" to a phone with BT

Hello
I recently bought a Go Color 7.
I can connect to my phone hotspot through Wifi and I can pair it with the phone with bluetooth.
But as soon as I try to connect with bluetooth, the connection is cancelled after a couple of seconds.

I tried it with three different phone (2 of them after a factory reset).
My "Go Color 7" has the latest software.

Anything else to try before I send the device back and ask for my money back ?

Cheers,
Patrick