After deleting my music (by mistake) I can't download all my songs back onto my phone

I accidently deleted all my music off my phone.

I plugged my phone into my laptop to sync all the songs back on the phone.

When i checked the phone certain songs haven't gone back on the phone. They can be played on the laptop but they wont sync over and when I press the cloud button on the phone (to re-download) it wont do it.

It seems to be songs that I downloaded on my phone directly that have been effected.

How do I get the songs back onto my phone without buying them again

Please help!!