If they are yours because you paid for them, then sue them for withholding your property or charge them with theft of your property.
If, on the other hand, you did not pay for them and they were sent directly to the company who did pay for them, then it may be your own error for letting the company have the originals - if you could have avoided it.
I believe this is a very "French" way of controlling aviation personnel by denying personal qualifications and keeping them tied to employment with "Company-use only" qualifications.
This "Air France" method was hard fought against when JAR-66/EASA Part 66 was formed and it was deemed (then) to be against human rights because it stifled the free movement of aviation personnel.
...maybe you could try that approach?