Tax free Rome

Good afternoon.26.09.2021 we made a purchase in your store in Rome. Тwo new iPhones 13 of 128 gb were bought.26.09.2021 we made a purchase in your store in Rome. two new iPhones 13 of 128 gb were bought.  We asked to issue a tax free check for a refund, the consultant made us a check. Upon return to Ukraine, at the airport in Rome, when we went to the service tax free refund, we were informed that the tax free check is not valid.  Thus we could not get our money back (428.82€) due to a mistake of your employee. How can we resolve this issue now? 

Thank you for your attention, we look forward to your support.

[Image Edited by Moderator to Remove Personal Information]