Totally confused about using Pandora, playing their music on Apple Car Play and data usage each time

I have updated my life and am now confused.

I subscribe to Pandora, and play the music through Apple Car Play. I pay for the use of Pandora, and am now wondering if I am being charged for data each time I listen to music. It seems that I could be paying double.

I thought that if I am paying for the data via my phone then, it would be better to use iTunes since I have already purchased a chunk of music about 8 yrs. ago. Now, I am reading that iTunes is pretty much history and if I did not backup my library then, it is in music heaven. Not good, Like someone else, I have the library on an my old Mac Donald- excuse me, on an Old Mac that is dead. If I could get to the hard drive I suppose I could retrieve what I had. I was thinking it was still in the Apple cloud.

So, for the first question- I pay for use of Pandora, play my music, and I noticed that my data amount was out of this world so, the large amount of data used must be from playing music. I do not text often nor talk much. I have this high priced phone for the bells and whistles.

I have considered using an Ipod to play music but, I see that they have become extinct like my iTunes. I do not mind paying for something that will continue to be mine and will stay with me. I don't care to make everyone rich because I am not too tech savy.

Any advice, suggestions will be appreciated.

Thank you.