Tash - a friend had a cat with similar problems but he was really long haired. She did just as you are doing - trying to associate brushing with food. She used soft cat treats that he loved. It did work but it took about 4 - 6 months before he was somewhat comfortable with it. He never did get completely comfortable with brushing. Also - she started with a visit to the vet. The vet cut out all the matted hair and snarls so that when she started trying to brush him it didn't really pull and hurt too much.
Now my 2 cats are different. If I get the brush out they will rub up against it they love it so - but they have never been abused either.

Hope this helps
Kathleen