Terrible service with saa

What is the use of your online check in if you change our seats last minute??? I sat and waited for check in to get a good seat. I booked my seat at check in time. Then you push me to the back. Also you take my luggage away from me yet your check in counter marked it as hand luggage. It met the dimensions and weight. Why did you inconvenience me? It's no wonder you guys are under business rescue.. You have a lot to learn from airlines like British airways and Emirates.. I'm furious right now. I booked saa and I thought it would be premium.. Why did you do what you did.. Why take my luggage away from me. It's hand luggage.