As a matter of fact, they do send an annual statement, at least they did last year. On 25th July 2017 I received a statement from Canva stating the withholdings from 1st July 2016 till 30th June 2017. Their accountancy year ends in June, so I expected to receive another one a few days ago. Nothing yet ...
With this piece of paper, my accountant can deduct the paid taxes from what I have to pay in taxes, though it's a very late deduction, as I will only see the results of the second half of 2018 in 2020 ...