Refusing to repair my iPhone 6

During the month of September I took my iPhone 6 for repair at Campus Square. The problem with my phone is: When someone tries to call me I can't hear them clearly even if the volume of speaker is on maximum volume. So to my surprise I got a quote from Vodacom says that \Screen cracked quote for a new unit R4k"Why?? Can't they fix/exchange the speaker? Yes the screen is cracked at the bottom left"