Capita cancelled PIP assessment - money stopped!

A good friend of mine has mental health problems, and was originally on DLA low care and mobility. He had a review a couple of years back, filled in the forms himself, and was reduced to just the low care, but was going through a really bad patch, and didn't fight it.
In february, he was sent the DLA to PIP forms and, with my adice, came onto B&W, and found out how to fill in his forms properly. He also had his local CAB check them before sending them off.
He then heard from Capita, telling him he had a face-to-face assessment, at his brothers home where he was staying temporarily, last week.
I warned him to have someone with him, and his brother took a day off work to be with him.
The assessor didn't turn up, so his brother phoned Capita to find out why, and it turned out that the assessor got lost and couldn't find the house, so his brother was given an address by Capita, where his friend could write to, to give an explaination as to why the assessment wasn't done.
He wrote to them immediately, and sent his letter with Track and Trace, and saw the next day that it had been signed for.
This morning, he got a letter from Capita, telling him his money is being stopped, because he didn't attend the assessment!
His brother phoned them up, and it turned out that Capita had given him the wrong address to send the letter to but, rather than setting things right, it appears they are going to keep to their decision to stop his money - because they can't trace the letter, despite the fact that my friend has the proof that the letter was delivered to the address they had previously given to him, and that he has the name of the person who signed for it!
Does anybody on here know what my friend should do now, please - bearing in mind that he is suffering great stress over all of this, but needs the little money they were giving him, as he had to give up driving because of his meds, and so needs that money to be able to get around?
He had been given 4 weeks to appeal