Alyr

Hi I am self-employed in the UK. I work in fashion. I participated as a model in Paris Fashion Week last September. I was given a contract by a French modelling agency who did the A1 voucher for me. To the gross pay a small sum was added as vacation pay (1/2 day) and 25% was deducted as agency expenses. I got a Certificate of Residence in the UK to provide evidence of my tax residence status but by the time I got it the agency had already processed the payment and I paid tax in France as a non resident foreigner. The amount was below €500. Was the vacation pay also taxed? But my main question is how can I claim back the tax paid on the amount I received? I am not even sure I know at what rate I was taxed. Please advise.