Now there's a very convenient way that you may/may not have know, is using the new UKVI gov site. You can request for the documents as an online request but please makesure you clearly opt-out the option that it's not a withdrawal. I mentioned that on the comments section as well. First request didn't work out within 10 working days and there was another link to remind them with previous request details and original postal references. That worked out well for me and got the certificate back in the sign post within 4-5 days.
link to the gov site section: https://www.gov.uk/visa-documents-returned
Please remember to keep a note of all the postal references and above request references which you will need.
Cheers
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