SLC wanting proof of NI

Hi. I already got my student finance approved and have received payments, both loans and the uni tuition being payed (through SFW). However I got a letter from SLC saying I need to confirm my birthday to verify my National Insurance number. There's a form to sign to state my birthday is correct, but on it it says "Please provide documentary evidence of your National Insurance number if you are confirming that the details given above are correct." I'm not sure what it means by this? Do I have to mail them a photocopy of my NI letter? I don't want to send them the original document because it doesn't mention anything about them sending it back. It just confuses me because they already have it on my online application anyway. Thanks for any help.

Hi there, did the letter state this could be sent via post? Thanks, Jason

I'm not sure. They gave a return envelope so I can mail back the form I need to sign to confirm my birthday but it doesn't specify if I need to mail the proof of my NI.

Hi,
Just to confirm, you're being funded by Student Finance Wales?
Thanks,
Ross

Yes