British Gas. Warm Home Discount

I was told by British Gas they would phone the DWP about what benefit I get and gave my National Insurance Number.

Month or two later get a letter asking to send in evidence I get benefit so I send in a DLA letter.

Now they say the letter was not enough and I have two weeks to get the evidence and return the evidence.

I feel like just giving up on it and when I try to phone engaged constantly.

I get Income Support also so was I to send a letter from them? Recent letter asking to tell them the full household income so that mean a letter re my partners carers allowance