123, Azad Street
Subject: Letter of apology
Please accept my sincere apologies for my being unable to attend the interview you have called me for. We did have a brief conversation through phone and we had agreed upon a time this Thursday afternoon.
But due to some unexpected issue that sprung up at work and I am engaged in solving some oracle issue, which is very urgent for the company I am working for. Therefore I am afraid I cannot commit for anything else until the issue is solved and everything is up and running smoothly.
Once again, I apologize for the inconvenience and thank you sincerely for your time.