Your doctor doesn't "take" Medicare. He or she has opted out. You have Medicare Part B coverage. You've paid your bill. You should have been given a copy of the bill along with a copy of your doctor's letter, signed and dated, this includes date of service as well as the date your doctor declined Medicare participation. Now it's time to file for your reimbursement. My understanding is that one can file up to a year after the date after the medical service--ie. 7/7/14-7/7/15. But why wait so long?
The following gives the best chance to succeed on the first try. Also remember if you have secondary coverage, Medicare will forward the necessary information to them when you check that box.