Why does my harsh inner critic drown out positive Metta phrases for myself?

My inner critic is viciously harsh and keeps on informing me that I am undeserving. When I speak of Metta to myself, the phrases that are positive are meaningless and are drowned in criticism. I fear that this is too powerful a life theme of self-hatred that the practice won't be able to overcome. What can I do to evade the criticism so that true self- Compassion can be established? My name is Vikram, DOB 3rd August 1989. Time: 9:00 PM. Location: Gurgaon.