They can contact their energy company, they can get extra help if they are on a low income. The DLA will be backdated once it's sorted. They would benefit from going to have a chat with the CAB as well, they will do a benefit check to make sure they are getting all they are entitled to.
Having a private pension does not automatically exclude a person from pension credits. It's means tested - so amount of private pension and also any savings. It's paid at two rates - the guaranteed rate of pension credit, which won't apply, and the savings credit which is for people who have a higher income than the basic state pension, or who have an amount of savings. If they had both, then they would not qualify, but it they have spent their savings in the interim it would possibly be worth submitting a claim for pension credits as having spent them they may qualify due to their means being reduced.
Have they claimed their winter fuel payment? Also, if they haven't already, have a look at Warmfront. They assess homes for energy efficiency and if deemed not efficient grants are given to cover the costs for installing insulation/heating systems etc which can reduce heating costs significantly.
My dad is profoundly deaf and became partially blind almost overnight and gets nothing, NADA.
ATOS declared him fit for work, just after his employers officially sacked him for being disabled (that is currently going to tribunal) after he had been off for several months for being unable to drive and them refusing to redeploy him. Then he got the letter turning him down for DLA a few days later.