Worst service

Worst service ever from Mango Airlines. First my flight was delayed with an hour coming to Cape Town last week. Now I was moved to the back of the plane after I checked in online without anything been said when I handed in my luggage. If I wanted to sit at the back I wouldn't have checked in online. They know in advance how many wheelchair passengers they will have on a flight so prebook those seats so that other passengers don't have to be removed from their seats after they made the effort to check in online and be at the airport way in advance for the flight.???