if you look at any currency value graph you will see that a general downtrend in the value of the pound, but also you can see the day it tanked due to the result. there was a slight increase pre-referendum, but the amount it decreases by it still far lower than it had been for months
anyway to get back to the ons article, if you actually read it you will see clearly it states that:However, in the last few years the EC figures have been volatile and so a five-year average has been taken to better represent a “typical” contribution. and it provides a figure of ~13.5 after rebate
my issue with everything youve said isnt even the money, its the fact you either, as i said before, you didnt read the article, you didnt understand the article or you deliberately chose to be misleading