How to forward further documents without a reference number?

Hi

I would be grateful for advice.

My application was sent out on the 15th of October, the fee was deducted two weeks later but I still haven't received the acknowledgement letter (or email). My problem is that I have to send to HO a document which I didn't have at the time when my application was sent out by the NCS. Without the acknowledgement I do not know my reference number so I don't know what to do. Can anyone advise? I'm just scared to send the document without a reference number in case it gets lost and won't reach the caseworker.

Call HO and try to get HO reference.
Did you check your email(including junk mail) as they have started sending emails as well.