Sony Ericsson :: W995 / Entering Contact Numbers Failed?

My daughter's phone has started doing something very strange with her contacts - if you enter a number and save it - when you go back to that contact the number has changed - it seems to another number in her address book - it's really bonkers. The phone is only a couple of months old - should we send it back or is there anything we can do? Also she says she has problems hearing people she calls but his is probably a different issue.