Unable to download old iTunes purchases.

I recently upgraded to an IPhone 8 Plus. When setting up my new phone I restored my Apple ID which loaded all my apps, messages, photos ect as normal however a lot of my music has been lost.

Some songs I could see were available to re-download direct in the Music app, however were still missing.

I have since searched some albums and songs that are missing (that I purchased in the past) on iTunes in the hope that I can simply re-download them from there as it will know if I have paid for them. However, when finding a song it is labelled as ‘Purchased’ - and I am no able to re-download it nor can I find it anywhere on the Music app or anywhere else on my phone.

Any ideas?