Locks door in my face, suddenly can't exchange

I wanted to exchange a R1 400 shirt for one size smaller. When we got to the store, the power had just gone off for load shedding. The manager saw us walking to the door, but instead of acknowledging us, he closed the door. When I then showed he I wanted to talk, he responded by locking the door. I then knocked after which he did tell me to wait two hours until load shedding was over. The three of us waited and when we got back I told him I wanted to exchange the shirt. He then said it was OK. They didn't have another size. After the three hours three of us spent on this, he then told us to come back on Monday if we wanted to exchange the shirt for something else, because of a computer issue. He was rude and smug, aggressive and tried to look for reasons not to help us instead of trying to suggest solutions. I can't afford going back to a store after spending 9 person hours to just exchange a R1 400 shirt!!