Picture this: the phone rings, it's the ex, and the singer decides to answer it in front of his new girlfriend. "Me está hablando mi ex" (my ex is calling me), he says, then "Permíteme" (excuse me) and "Voy a ponerla en su lugar" (I'm going to put her in her place). What follows is one long, very petty phone call.
He opens with "¿Qué diablos quieres?" (what the hell do you want?) and "¿Qué parte del no no entiendes?" (what part of no don't you understand?), a phrase Spanish speakers use exactly like English speakers do. Then he twists the knife: "Te está escuchando quien te ha suplido" (the one who replaced you is listening), and she does it "mucho mejor que tú" (much better than you). Suplir means to stand in for or replace someone, a nice formal word to drop into a breakup.
The cruelest bit is the speakerphone. "Si quieres oír los besos no cuelgues, quédate ahí" (if you want to hear the kisses, don't hang up, stay there), and "Si quieres atormentarte pon el altavoz" (if you want to torture yourself, put it on speaker). He leaves the choice to her: "Te dejo a ti que decidas si vas a colgar o no" (I'll let you decide whether you hang up or not). Notice how many commands are packed in here, vete, quédate, pon, muere, which makes the song a great drill for the imperative.
He signs off with "Muere de celos y de rabia" (die of jealousy and rage), because "al cabo que no sabes dónde estoy" (after all, you don't know where I am). Al cabo que is a very Mexican way of saying "anyway" or "after all". It's a bit much, honestly, and that is the fun of it.