This was also my experience and my head was ready to explode. (I had a schedule change which resulted in an illegal connection. They eventually understood the issue and managed to rebook us at no cost - after hours of calls. However they repeatedly failed to reticket the reservation and the airline kept cancelling it.). I would demand a US-based supervisor but only occasionally was successful. Eventually I sent a half dozen messages via LinkedIn to senior executives I could identify and got a couple who replied and who had the right person (from the US) call me and fix things. When I asked for compensation they actually shocked me with a very generous return of points - which went a long way toward showing they felt bad (but didn’t eliminate the pain I endured). Like you I vowed never again. I was told that they had many passengers not as savvy as me who didn’t know they had not been ticketed showing up at the airport and discovering they had no reservation.