SAN DIEGO -- Travis King is proud of his military service, and he said he would still be on the front lines if he could. King's military career was cut short by a frightening diagnosis.

"I had double vision, and that basically was a red flag for me," the former Marine staff sergeant said.

The double vision turned into lost feeling in his face, and, eventually, he was told he had a brain tumor.

"Hearing brain tumor ... I thought he was going to die," said King's wife, Trina.

King endured months of treatments, two brain surgeries and radiation. The tumor was gone, and he was medically retired from the Marines.

"I thought everything was okay," he said.

A few months after his retirement ceremony, King started receiving medical bills in the mail, with the amount adding up to more than $15,000.

"He had emergency room visits, urgent care visits, lab work," explained Trina King.

They thought those visits would be covered by insurance they had purchased before King retired from the Marines. King paid for one year upfront of the insurance, TriCare. However, TriCare only works if the retired service member is also signed up for Medicare.

"I thought I had Medicare" King said.

It turned out he didn't have it and he needed to sign up for Medicare before he retired, but King said he never heard that.

He did receive a warning letter from the Department of Defense, but it came three months too late. King retired in March, the letter arrived in June, and his Medicare enrollment ability had lapsed.

The Kings said they attempted to fix the problem, making multiple calls and writing multiple letters to Social Security and Medicare, but their attempts failed.

"All you can do is write another letter, send another form," Trina King said.

The 10News I-Team made calls on King's behalf to cut through the red tape. The I-Team called Camp Pendleton, the Department of Defense and Rep. Bob Filner, who chairs the Veterans' Affairs Committee, Social Security and Medicare, which assigned a case worker.

The I-Team learned that what the King's experienced is not an isolated event. There has been a problem with military veterans not signing up for the correct Medicare program before they leave the service and there is also no quick fix.

"It's easy to fall through the cracks and nobody is helping you and you start to get these bills," King said.

The good news is that Medicare was able to help after the I-Team's call. Last week King was enrolled and his medical bills are being sorted out.

Although he could've stayed on disability, he just took an aerospace job and now has private insurance along with Medicare.