Contradiction with Job 30:20
While Psalms 91:15 promises that God will answer when called upon, Job expresses that he cries out to God, but receives no answer.
Job 30:20: I cry unto thee, and thou dost not hear me: I stand up, and thou regardest me [not].
Contradiction with Isaiah 1:15
In contrast to Psalms 91:15's assurance of God listening, Isaiah describes a situation where God will hide His eyes and not listen, even when many prayers are offered.
Isaiah 1:15: And when ye spread forth your hands, I will hide mine eyes from you: yea, when ye make many prayers, I will not hear: your hands are full of blood. [make...: Heb. multiply prayer] [blood: Heb. bloods]
Contradiction with Lamentations 3:8
Psalms 91:15 guarantees God's response, whereas in Lamentations, the speaker feels shut off from God, with prayers blocked.
Lamentations 3:8: Also when I cry and shout, he shutteth out my prayer.
Contradiction with Micah 3:4
Psalms 91:15 assures divine response to calls for help, but Micah states that God will not hear or respond in times of distress due to the people's evil deeds.
Micah 3:4: Then shall they cry unto the LORD, but he will not hear them: he will even hide his face from them at that time, as they have behaved themselves ill in their doings.