CLS Shooting Brake 2015 (X218) - aux in low volume - HELP!

[mrpotatohead]

Hi All,
Newbie to Merc's and the site so bear with me!
Recently purchased a 2015 CLS Shooting Brake.
I've noticed that when I have my iphone (8) plugged into the USB in the centre console that I CAN'T control the volume on the phone or car when playing back tracks from Spotify.
The music itself plays and I can switch between tracks etc using COMAND - I just can't adjust the volume AT ALL.
Any advice?
Thanks

 

[DavidPreston]

Sorry, l have the same car but haven’t had any problems with Spotify. Volume is controllable from the steering wheel but l haven’t used the phone buttons for volume.