call center agents are of no help for this issue for award flights. they will only rebook if the same award class is open on the desired flights. they have no power to book into other award fare buckets or open a promo reward seat on the flight.
only backoffice in IST or a local sales office or filling out a feedback form can help.

usually you should be able to search for yourself on the website to rebook your flight. in case you don't find anything that you desire contact your local TK sales office.