Paid Seats

Flying Safair quite regularly between PE and CPT, and as I understand one pays for selecting a specific seat. I normally also check in online as soon as it opens to secure my seat. Today I get to boarding gate with my ticket for 3D and I get told I'm now sitting in 22A at the back. ***? Moved for balancing purposes... Then to be fair everyone should be moved, not so? What's the use of giving clients the option if it means nothing. I'd rather pay more and get what I pay for... Back to SAA for me!