problem with meizu pro 5

I upgraded my Meizu pro 5 to Ubuntu Touch 16.04(r155), but now I cannot roll back to the stable version 15.04. Even with the developer mode enabled the phone isn't recognized by my computer.
When i'am trying pass in develper mode , the phone is not reconized by the computer and i cannot use the ubuntu-device-flash touch --channel=CHANNEL command to roll back.