Hi, 
It seems that the Home Office sends the certificates before they let you know the application has been approved. 
In my case, I received the approval/invitation to book a ceremony on the 28th of February. I celebrated but couldn't book ceremony as 'details could not be fetched' from the council page. Waited for a couple of more days but still was unable to book. 
I contacted the council asking how long would I need to wait. For my surprise, they told me that my certificates (mine and my children's) were returned to HomeOffice at their request on the 28/02 (same day I got approval).
Then he adds that I have 6 months to book ceremony from 16th of February (meaning that they actually got the certificate on that date!). 
I'ts been a week since I got my approval/invitation to book a ceremony but I am not able to do so because council sent back my certificates and home office does not answer nor reply to 
citizenship.support@homeoffice.co.uk. 
Not sure what to think off and I am losing my head around what could have gone wrong for them to 'request' the certificates without giving the council explanation!. 
I am crossed!