SEAT ALLOCATIONS

Me and my family booked a flight on Lift (confirmation attached) on the 31 December 2020 form George to Johannesburg. We are a family of 6 and reserved and paid extra for seat reservations in order for our family to sit together. But when we got to the airport and collected our border passes, our seats were reallocated which left us with my small child in the back of the aircraft while I was sitting in front!!!! How is it possible that I reserve seats AND PAY EXTRA FOR IT just to be reallocated????