Where to send supporting documents to

So I submitted my passport application 12 weeks ago ahead of my wedding with a PD2 form to change my name. After a lot of chasing I have found out that they now want to see my marriage certificate as the whole process has taken so long that I am now married. They said they sent me a letter over a week ago but I haven’t received it and I can’t get anyone to send me a copy or tell me where to send my certificate to. It’s now only three weeks until I’m supposed to travel on honeymoon so can’t afford to send my certificate to the wrong place or to wait for a letter which I doubt will arrive! Please can anyone advise where I would need to send my certificate to if my application is at Durham and also if there is anything I can do to speed up them processing the certificate? Thanks so much for your help as I’m at my wits end and have no idea where to turn!