I boarded the 02:40 flight to Zanzibar on 2nd October 2019. I was shocked to find that the aircraft supervisor told me that I cannot pay for the extra legroom emergency exit seats, even though they were on for sale, something that I have always paid for. I told the the steward (Philipino lady) that I want to pay for it. She then said she had to speak to the Captain if he will allow it. I then challenged her to goto speak to the Captain if that's what she needed to do. To be it was bizarre, as I paid for these seats many times before. Now all all of a sudden apparently thr captain needs to approve it to "have optimum weight distribution". Im no pilot, but even I know that the only place that you want weight in an aircraft is in the middle above the wings!. The steward then proceeded to delay taking the payment so that she could wake me up from my sleep. Thr steward then kept on knocking me with the trolley every time she went down the aisle, disturbing my sleep. I think the other staff in flydubai are excellent, however next time if I see this steward, I will make a complaint to the Captain and let him know what happened the previous time. This must not happen again. This steward is on a power trip.