Seventy-four-year-old T.W. Aldridge of Mississippi woke up one day to discover he'd suddenly been switched from the government-run Medicare to a private Medicare Advantage plan. A con artist insurance salesman had forged his signature in order to collect a $300 commission, putting an ailing Aldridge in a plan his son says his doctors would not accept, CBS News chief investigative correspondent Armen Keteyian reports. 

"He told the doctor 'I can't go to the hospital. I don't even have insurance, they got me so fouled up,'" said T.W.'s son, Mark Aldridge. 

A CBS News investigation has found Medicare Advantage has become a costly disadvantage for tens of thousands of seniors who unknowingly wind up on a private plans they don't want or need, hooked by unscrupulous salesman. 

At the Medicare Rights Center, complaints pour in daily about tactics used by some of the 200,000 agents pushing private Medicare plans nationwide. 

"Insurance companies are doing very well quarter by quarter thanks to these programs," says the center's Robert Hayes. "Brokers, who are often pretty much unregulated in most parts of the country are going around, working on high commissions." 

To date, 43 states have received complaints about people being coerced or conned into private Medicare plans. The complaints include forged signatures, identity theft, lying about coverage and illegal high-pressure door-to-door sales tactics. 

Leslie Norwalk, the head of Medicare, says her agency is cracking down on deceptive sales practices. 

Keteyian told her: "We got a woman in Kentucky who had to call 9-1-1 to get the salesman out of her house. We have another case where agents are signing up dead people in Georgia. We have another case in Mississippi where 100 people whose IDs were stolen, they turned up on Medicare Advantage. I mean, when you hear things like that..." 

"I'm glad that we have such competent law enforcement partners and that we work together with them as soon as we hear of these things," Norwalk said. 

CBS News has learned that, overall, at least 36,000 seniors have pulled out of their private Medicare plans in just the first four months of this year. And nearly 100 private plans have been ordered by Medicare to change the way they do business. 

Find resources for navigating private Medicare. 

Like so many others, T.W. Aldridge tried to get off Medicare Advantage through months of phone calls and letters to Medicare and the private plan. He finally did. Ironically, it was 11 days after he died last August. 

"The last thing that he said was 'take care of your mom, make sure you take care of those bills. Don't leave all those on her,'" his son said. 

Forty thousand dollars in bills that remain a family burden — bills that Medicare has yet to pay.