I wouldn't rely on any info from TK call center agent about this. Most likely they will misunderstand your Q or provide misleading info. You should understand that this is TK and there is a high risk that what you have been told will not be the outcome, if you expect to cancel and get a full refund very shortly before departure.

My guess is that you can cancel for a full refund up until departure and even after no-show (unless no-show fee is stipulated in the fare rules) but admittedly I have no first hand experience with this, so you shouldn't rely on this.