The ringtones you purchased should be redownloaded to your iPhone. If your ringtones don't download, it could be because they're no longer available on iTunes or, as SravanKra suggests, because you're not signed in with the Apple ID that you purchased the ringtones with. I purchased a ringtone from iTunes on my iPhone 6 and I can't find it anywhere, not even in the folder I purchased. I can find the ringtone I purchased in the Itunes app on my iPhone, but I can't find the ringtone to apply to a contact.
If the ringtones are the ones you downloaded yourself and imported into iTunes, you must connect your iPhone and synchronize the ringtones with your iPhone.
