Low quality iOS

[user-removed]

I'm having problems with sound quality. The songs play with a squeak like a poorly tuned radio. Very low sound quality.
I have the Family Premium Plan and this only happens when I listen on my cell phone (iPhone 6) using the data network.
I have tried everything but nothing works: Setting the Equalizer (from the phone and the application), reinstalling Spotify, check with my mobile operator (I have an unlimited 10Mbps plan), configuration of the transmission quality, etc.
Does anyone have a solution?