Atormentarte comes from the verb atormentar, meaning 'to torment' or 'to torture'. The -te ending makes it reflexive, so it means 'to torment yourself'.
In the song, the singer is speaking to an ex-lover who has called. The line "Si quieres atormentarte pon el altavoz" (If you want to torment yourself, put it on speakerphone) is a defiant challenge, daring the ex to listen to the new couple's happiness and suffer from jealousy. It's a strong, emotionally charged word that captures the song's dramatic tension.
Ever had an ex who just won't quit calling? Moderatto totally gets it in "Llamada De Mi Ex" [My Ex's Call]. The song kicks off with the singer's ex on the line, and he's not having it. He's ready to put her in her place, asking, "Qué diablos quieres? Qué parte del no, no entiendes?" [What the hell do you want? What part of no don't you understand?].
It's a super blunt and funny take on moving on. He tells his ex to go with whoever she wants and never call again because his new partner is listening and, frankly, "lo hace mucho mejor que tú" [does it much better than you]. He even dares her to stay on the line if she wants to hear them kissing! He's so over it, he tells her, "No puedo perder el tiempo ella me hace feliz" [I can't waste time, she makes me happy]. He even suggests she put him on speaker and "muere de celos y rabia" [die of jealousy and rage] because she doesn't even know where he is. Talk about a mic drop!