Cancelled booking

I booked a trip for my daughter and I from Umtata to Pretoria traveling yesterday. I checked in at the required time and even received bag tags for both her and me. Upon getting to our destination seats other people were already seated. I went to the bus drivers to question this and to my surprise I was informed that my daughters ticket was cancelled. I was surprised because I know for a fact that I didn’t cancel the ticket. I was also informed that the ticket was cancelled via this call centre. I still told them that I didn’t cancel. They said the ticket was still open so hey reissued a new one for me but we had to sit separately. They said I was lucky because the bus not full. I had to ask the gentleman sitting in my designated seat to move and he agreed. I am not happy with this and I need questions answered. How do I check in if the so called ticket is cancelled? Who was given authority to cancel my ticket? I’m really not happy with this service. The ticket number in question is TB02QFAC.