SAN DIEGO -- Isabella Depierro's nightmare began last fall.

"I got a call from the collection agency telling me, 'You didn't make this month's payment. You're past due. You need to make a payment,'" Depierro said. "I can't even explain to you how frustrated and violated I felt."

Depierro received a bill from a collection agency -- first, $470 for a visit to the emergency room she never made. Then, a second bill came for services she never got.

"I called UCSD's billing department. I was bounced back and forth, from collections to billing. I finally gave up," she said.

The University of California, San Diego's billing department told Depierro the issue was out of its hands.

"They just told me, 'We're sorry, it's not our problem. If it says that it's you, it's you.' There's no way to prove it," Depierro said.

Depierro went to UCSD in person, asking for information on her medical visits.

She filled out a form and within minutes she had her file.

"I walked out the door, no ID check, no nothing," said Depierro.

That is when 10News Investigates became involved.

Investigative reporter Elizabeth Sanchez went to UCSD to find out what was going on.

"What went wrong here?" Sanchez asked Kathleen Naughton of UCSD.

Naughton replied, "I really don't know the answer to that question. Our procedures are to ask for a photo ID."

10News determined that if UCSD never checked Depierro's ID in order to get her medical records, then there is a good chance any imposter would be able to do the exact same thing.

Pam Dixon of the World Privacy Forum took a look at Depierro's records. The records showed that the imposter went to the ER to get pain medication for a backache and toothache.

"Your medical file, which already existed at this hospital, has now been combined with that of a criminal with drug-seeking behavior search for Vicodin and all sorts of pain medications," said Dixon.

Medical identity thieves use any piece of information; in some cases, just a name, birth date and address, according to Dixon.

UCSD is mandated to treat everyone that comes into their emergency room, Naughton said.

"So, someone can receive treatment without a photo ID?" Sanchez asked Naughton.

"It would definitely be possible, yes," said Naughton.

UCSD told 10News this was its first case of medical ID theft. Officials were quick to point out that they prefer a photo ID to identify someone.

However, that did not happen for Depierro.

So, what about Depierro's medical records?

10News was told that the employee that handed over the medical records has been disciplined.

Naughton said, "All of the staff has had a policy review."

Margaret Douglas was apprehended on charges of impersonating another woman to get drugs from a hospital emergency room.

"The doctors at Scripps started to recognize her from her multiple visits. They put 2 and 2 together," said deputy district attorney David Uyar. "She would come into Scripps complaining about either a toothache or backache."

The person resembles Depierro's alleged impersonator.

10News found out that Douglas went to the same high school as Depierro. In fact, Douglas' other victim also went to Chula Vista High School.

10News Investigates told the Chula Vista Police Department about Depierro's case and department is continuing its investigation.

UCSD has removed the ER bills from Depierro's record and acknowledged that she was a victim of medical ID theft.

She said her credit report is messed up and her FICA score has gone down.

"It's always going to be there. Of course it's going to follow me," said Depierro.

UCSD officials told 10News that it was in the process of improving its system to check identities.

New software is due to be activated, UCSD officials said.

Officials promised 10News any future medical ID theft victims would be referred to in-house privacy experts.

Privacy experts advise people to look for anything suspicious in statements from health insurance providers.

Also, experts recommend checking credit reports regularly to protect yourself from possible ID theft.