Special support element

I have applied for the special support element of the loan due to pip an esa, but my evidence keeps being rejected.
I phoned the DWP and asked for a letter as evidence, they told me the letter they provided was the only thing that could be sent. The letter states the date I started receiving the benefit and that it is for an ongoing period. But the letter is still not accepted, and I am being asked for a letter that proves eligibility during the academic year.
Where and how can I get a letter from that proves this?

Thanks