Nkazimulo's "Promise" is about being unable to let go of someone long after the relationship has ended. The speaker opens by wishing for a rubber band on their wrist, a trick people use to snap themselves out of a habit, because they keep thinking about this person and keep writing poems about them. They even admit they still say they're in love.
The turning point comes with the phone call. The speaker still has the number saved, tries it, and hears a recorded message saying it doesn't exist. That flat, automated voice, set apart in capitals, makes the loss feel final, and it leads the speaker to a darker thought: maybe the kind of love they're looking for doesn't exist either.
The mood is tired and quietly sad. The speaker sounds "battered and bruised," ready to give up, and regretful about a missed chance to hold this person close. The last line explains the whole poem: the words come "straight from my blues," so the sudden confession is really just pain finally spoken aloud.