cannot change seat numbers

On the 12/02/2015 I booked 3 tickets for 50 shades of grey in isle E, seat 3, 4, and 5. ticket date was for the 13/02/2015 at 17:15. on the 13/02/2015 I wanted to book another 2 tickets, and then change the seating arrangement so 5 people could sit together, this they could not do. we then went to the self service booking to have a look at the availability of seats, and 50% of the cinema had not yet been booked???? they refused to change the seat numbers, their was no excuse given, no explanation etc... they simply were not willing to assist at all. how and why is this possible. I find that to be extremely terrible service considering that between 5 people R500 was easily spent on the night in question. we are charged ridiculous prices for pop corn and drinks etc... but Ster Kinekor could not assist the paying customer. If the cinema was fully booked I can understand - however as I have indicated, half the cinema was empty.