Q: library

Download Past Purchases

http://support.apple.com/kb/HT2519

Whether you need to pay to re-download a song depends upon what country that you are in - does the song appear under Purchased link under Quick Links on the right-hand side of the iTunes store homepage on your computer's iTunes : re-downloading ?

Songs won't automatically download, only future purchases will automatically download if you turn on automatic downloads on your phone/computer e.g. if you buy a song on your computer and you have it turned 'on' on your phone then it should download on your phone.

If your account is still based in Canada then on your iPhone they should show in the Purchased tab at the bottom of the iTunes store app