I Was Charged for Free SunExpress Online Check-In and My Family Can't Sit Together

On the SunExpress website, it states that online check-in is free, but when I completed the online check-in, I was charged a fee per passenger. I purchased tickets for my wife and our 4-year-old son. When I called customer service, they told me that if the system assigns seats automatically, it doesn't consider the child's age; the child is seated wherever the system places them. So, does that mean my wife and young son could end up sitting separately, possibly far apart on the plane? At this level of technology, such poor service is unacceptable. I even had to pay extra fees for a process I completed myself. Additionally, when I called customer service, I was charged per minute outside of my regular plan, even if the amount was small. I regret buying the ticket. This experience has been extremely disappointing.