Warm home discount

I have for past 5 or 6 years claimed warm home discount successfully via edf energy. Last year as they changed things I awaited letter but nothing came. I contacted gvmt helpline, they said i was eligible and would sort claim. Months went by then a letter asking for proof of benefit (working tax credits) and energy account details. Supplied and sent back. Now asking again for same thing despite supplying twice. Can send photo of letter. Any ideas on how to proceed?

Thanks gordon, unfortunatly the government have closed the helpline so only answer letters about 2 - 3 months later.