EEA2 RC - original marriage certificate not returned

[KarmaPolice]

Hi,

my (non-EEA) spouse has applied for a RC in February. As we intend to travel before August (a close friend is getting married) and her FP has expired, we have requested our passports and wedding certificate, which is in Farsi to be returned including the translation.

A week later the passports were returned as requested, however only the translation of the wedding certificate was returned and they kept the original.

We have sent another request to return the document, and followed it up after 10 days (using the web form) but have yet to receive a response from Home Office.

Questions:
1) Is there a reason for them to keep the original document (even though it is in a foreign language)?
2) Can we apply for a new FP without it?
3) Is there any chance to speed up the application process by stating the circumstances to the case worker?

Any help is much appreciated