why cant i acess music i bought on the past in my new iphone

Seems you would need to use the same Apple ID that was used for the purchases.

Apple Support has an article online that may help REdownload the music:

Redownload music - Apple Support

and

What to do: If there's an issue when you re-download apps, films or other content from Apple – Apple Support

Your purchases are tied to the Apple ID that you used during the past 10 years. Use the same Apple ID for Purchases and you should see that music available for download.

Axel F.