need advice

[mrclean6507]

i just recently had a service connected disability changed to 50%, but should have been done when i retired in Sept 2004, i had sleep apnea since 2001, and have the documentation for it. i joined the va in december of 2008, not knowing i had to when i retired. the AF did the testing on me but never gave me the CPAP machine which when i did get it in Dec 2008 thats when my rating went up. can i go back and get what should have been payed to me since Sept2004. how do i do this or who do i talk to? any advice