Spotify on my iPhone doesn't recognise me as premium user

[toe-knee]

I'm a premium user and Spotify works fine on my desktop mac pro but on my iPhone, although it shows my playlists (all listed as havng 0 tracks), I can't play them it tells me I must be a Premium user to listen to radio.

I can't see anything in Settings that will allow me to enter authenication information so don't know what I can do to fix this!!?

I've asked all my Spotify using freinds but they're as confused as me.

Can anyone steer me right?

toe-knee