Husband's PIP stopped except standard rate mobility

Hello, my hubbie had one total new knee replacement, and was awarded full mobility and full disability, then was reduced to standard exactly a year later had to have another total new knee replacement but was kept on standard rate, November last year we informed them that my husband had been diagnosed with severe sleep apnoe and was put on a cpac machine all night,an assessor came out supposedly to register the machines number, my husband also suffers from severe depression and has been under a crisis team, beginning of January after this assessor had blatantly not listened at all to my husbands needs and mental health decided to stop all his pip except for standard rate mobility, was this decision acceptable we did write a letter to appeal but they came back with the same decision, this as had a severe affect on his mental wellbeing, and he has to have another knee operation on Nov 2 and as previous one has not worked  Thankyou