hang up, call again - and make sure they understand that the rebooking is involuntary because they have cancelled a confirmed flight.
agents can do almost everything without any fees when they correctly add the phrase "INVOL NO ADC.INVOL DUE TO FLIGHT CNX."
if there is no award availability on the intended flights you have to open a feedback process via the feedback form or contact a turkish airlines sales office (see below)
https://www.flyertalk.com/forum/32802016-post7.html
In case of an involuntary situation, you would have the right to change your award ticket to any Turkish Airlines/AnadoluJet flight within the -7/+30 day period of your original flight without any extra charge and regardless of award inventory. Plus, you would be permitted to make origin/destination changes within the same region. Although, to rebook, you might need to call the hotline to make these changes. There were some reports here in FlyerTalk that the hotline agents were refusing to rebook passengers in flights that don’t have award availability during the rebooking process; this is not true, although as hotline agents do not have the power to open up award availability, you would either need to fill out a feedback form or contact a sales office for rebooking on a flight that has no award availability. If you would like to rebook on another airline when EC 261/2004 or Turkish SHGM regulations apply, you would need to fill out a feedback form or contact a sales office; hotline agents are not permitted to rebook passengers on other airlines.
this rule is in line with the passenger rights - section "cancellation of flights"
https://cdn.turkishairlines.com/m/27...NG-ee-copy.PDF