I just wanted to share my experience in case someone else will benefit. I am flying from Ohio to Istanbul through Chicago. The flight from my home airport to Chicago is with United Airlines. Both flights are on one ticket. My original flight to Chicago was cancelled. I was placed on an earlier flight the same day. However, I could not confirm the change on the website so I called them. The agent stated that in order to get the ticket from Ohio to Chicago issued I would have to go in person to a Turkish Airlines Sales Office. The nearest office is in Chicago 6 hours by car. : )
I was then instructed to send emails to Chicago office and fill out an online request at Turkish Airlines website.
I did that but then I was able to find the phone number to the office in Chicago and I called them. A very pleasant agent was able to issue the ticket electronically. She advised me to call United and confirm with them that I am on the flight. I did, and I am.
Just in case this happens to you, don't get anxious. Call the appropriate local sales office and they will help you.