BA flight DUR-CPT seat changes

On a recent flight from Durban to Cape Town, I checked in online and chose seats on aisle 4 for my wife, myself, my 5 month old daughter and my 3 year old son. We choose the front seats as it's more convenient especially for the kids. When checking in our luggage at the airport, I discover on our printed tickets that our seats were changed to aisle 22. I enquired with the lady at the front desk and she said our seats were changed because Business Class was extended to aisle 4. This was done without notification to me or even an apology. We even enquired with the aircraft attendants if we could get a seat closer to the front but no BA personnel was even close to being helpful. I'm disappointed at BA, we've had numerous flights and have been happy but this has spoilt my experience with BA, especially the fact that I wasn't notified of the change or that no one was even slightly apologetic about it.