I’m betting you didn’t select DTS on the DVD audio set menu. DTS is ‘usually’ an optional format for the few disks that have it. DD and DTS are both on the disk and you have to tell the player which format you want to listen to.

If you are selecting DTS and your display still shows Dolby, I’m guessing your display is messed up. Dolby can not extract DTS coding. Both formats are proprietary from what I understand.