Perhaps you misheard? http://www.lyricsmania.com/feuer_lyrics_marteria.html
Hmm, that's not really clear enough to me to be able to say that it's definitely der... Based on the fact that it would be grammatically incorrect were that the case, I suppose the intended meaning is something else but it's just not enunciated clearly due to some combination of singing/slang/accent. Ok, it could be genitive plural... but that doesn't seem to fit the context of the preceding lyrics.
Flame is 'die Flamme' and they're conceptually different. Flame/Flamme is a regular noun, whereas fire/Feuer is abstract, like light/Licht, air/Luft, or nature/Nature. You can refer to fire as 'fire' or 'Feuer', without an article, for example 'Fire is hot'/'Feuer ist heiss', the same way you can say 'Light is bright'/'Licht ist hell'.
But you can't do this with Flamme. You have to say 'The flame is hot'/'Die Flamme ist heiss' or use the plural 'Flames are hot'/'Flammen sind heiss'. Thus, they're different things.
You could also approach the question ontologically and say that while fire is made of flames, a flame is an instance of fire, the same way traffic/Verkehr is made up of vehicles/Fahrzeuge, while a vehicle/ein Fahrzeug is an instance of traffic/Verkehr.