reinstating PIP

I am the appointee for my son who suffers from severe mental health problems as well as an acquired brain injury.
He was getting PIP at the full rate he went missing and was homeless over 12 months ago. He was eventually picked up at the otherside of the country.
He was in crises very psychotic and a danger to himself and others. As a place of safety he was put in Bellmarsh prison until a mental health bed could be found in Lancashire.
They stopped his pit somethig I did not realise for some 3 months and his Universal credit. After a lot of fighting I got his UC reinstated.
I understood that he was in hospital he would not be eligible for the care component but was told eventually by someone at the DWP he was eligible for the mobility part . They paid him this for a few months and then they just stopped it not letter informing him so no decision to ask for a mandatory reconsideration on. He has now moved to independent living as such I feel the whole award should be reinstated.
I am in the process of contacting them but have been cut off every day this week.
Just wanted some thoughts before I finally get to speak to them. Any tips on how to contact the regard best time of day etc Thanks