I think you misunderstand — the government has little interest in making sure you get all your pay-ins back, and they are in fact trying not to, as if it were that way they would lose their giant slush-fund.
Secondly, Social Security has been absolutely fantastic in making the elderly dependent on the government, just like welfare does for the poor, and just like welfare there's a huge incentive to nurture and grow that dependency apart from all the corruption and control issues: if the agency were to adequately address the issues they were set up for, their utility would go down and the bureaucracies would be cut.
It is indeed a scam.
Welcome to FR!