@sojab0on Audio speakers works generally over bluetooth, but audio calls (2 ways audio flux) is not working. That is a well known issue. To help with your problem, I can suggest wired headsets. I use the earplug from the PlayStation 4 controller and I'm satisfied with this solution. But there are other wired solutions... until this bug is fixed. But old kernel means old bluetooth support, so I'm not convinced it will be fixed soon, but one can hope.

@sojab0on Hands free doesn't work in Ubuntu Touch. Lots of users are frustrated by the absence of the feature. Bleutooth connection mostly works and the music audio protocol operates correctly. Speech conversation does not. It may be that the SCO channel capability is not enabled: or that it is enabled and not found: or that it is enables and found but that the necessary codec is not enabled or is not found... There may be a very simple fix but whatever the answer, it needs a mini project team of specialists - which we don't have. Hopefully such a team will form