Name the missed agreement before judging the person’s entire attitude.

One broken arrangement is easier to fix than a diagnosed character. When somebody misses what they said they would do, the mind jumps quickly to a general finding about how little they care, and once that finding is stated aloud the conversation is about who they are rather than about Thursday. People can correct an action, but almost nobody can defend against a verdict on their nature.

Say the specific thing. You said you would call the plumber and it did not happen. Then stop and let them answer, and see whether the reason is what you assumed. Keep the wider theory to yourself until one instance becomes a pattern.