I am sorry to hear you have having problems with Jess. My name is***** am a veterinarian, and will do my best to help.
Does he have long hair?
The best way to deal with these mats or clumps is to prevent them by regular combing, to remove the loose hair. I like a tool called a Furminator. It removes loose hair better than anything else I have used.
Once a clump has formed, sometimes you can work it loose with this tool, but large mats have to be shaved off.
Older cats like Jess sometimes are not grooming as well, and will develop these clumps more than when they were young. It may be they have arthritis, and it hurts to reach their backs. Some cats get too heavy to be able to groom well.
yes he does i have been doing all of the above,