We had to use Turkish air out of Istanbul last year, booked by a TA, with oceania air. Will never fly Turkish air again, if I can avoid them. TA and Oceania air dept could not contact Turkish air to upgrade seats. I attempted to call many times, their customer service is a joke. We were able to upgrade all other flights, just Turkish air. Security at airport was kinda crazy too, maybe it was a bad day.
We have a cruise in 6 weeks. Had TA contact Oceania air dept, to get flights ticketed. They did and I was able to upgrade seats on Delta and Iceland air.