I had the same problem but found it at the bottom of the letter which was with the 4 page coloured newsletter.
[email protected]
You have to be careful the other side may have given you a wrong email address.
My understanding is that I think you may be too late to give the proxy form as it had to be in at 11.00am on 16 Jan 2018 some 45 minutes ago at NIU office at Belrose.
If you are a company then you can email the form to the above email with the attached voting form they sent you giving them authority to vote on your behalf.
Otherwise you can turn up on Thurs and vote at the meeting on 18 November.