Anthony Noto, CEO of SoFi Adam Jeffery | CNBC

Student loan refinancing companies say they offer borrowers a way to save thousands of dollars on their debt, by allowing them to pay off their loans at a lower interest rate, in less time. The reality can be much different. Recently, the government found that online lender SoFi was misleading consumers on how much they'll save if they refinance their student debt with them. The company's ads boasted average discounts of more than $22,000, but in its calculations the company excluded certain borrowers for whom refinancing resulted in a more expensive loan, the government found. In a settlement with the Federal Trade Commission, SoFi agreed to stop its misrepresentations. SoFi spokeswoman Brielle Villablanca said the company has always been committed to giving its current and prospective members clear and complete information, in a statement to CNBC.

The Federal Trade Commission found SoFi's advertisements misleading Source: SoFi.com

SoFi is not the only student loan refinancing company the government is monitoring, according to records obtained by CNBC though a Freedom of Information Act Request. The Federal Trade Commission recently sent "final warning" letters to other companies that offer big savings to student borrowers, CNBC has learned. Those lenders are CommonBond, Credible, LendKey and Splash Financial. "We strongly recommend that you review your own company's advertising claims to make sure you are not making false or unsubstantiated representations," the FTC wrote to these companies in October. The average graduate leaves school with $30,000 in debt, up from $10,000 in the early 1990s. The country's outstanding student loan balance is projected to swell to $2 trillion by 2022.

Mark Kantrowitz, student loan expert Source: Mark Kantrowitz

CommonBond previously advertised average savings of $24,000 on a page of its website, however that figure was removed after a CNBC reporter asked the company's CEO David Klein how the lender arrived at it. "You've caught a bug," Klein said. "We don't communicate average savings information. We believe every borrower is different." Credible, a marketplace for lenders, also removed its advertised average savings rate, which was over $18,000, the same day a CNBC reporter inquired about it. Stephen Dash, CEO of Credible, said the company decided to keep its advertisements more general in the wake of the FTC settlement. "It's not a one-size-fits-all," Dash said. LendKey's advertisements also made dramatic claims. In one, the company said people could reduce their monthly payments as much as 40 percent. An online ad for LendKey, which the company says it is trying to remove.

Lewis Goldman, the chief marketing officer at at LendKey, said they were working to take such old ads off the internet. "We don't make claims any more about absolute savings," Goldman said. The CEO of Splash Financial, Steven Muszynski, said its advertised savings rate of $29,340 is "very sporadically used." "We also are clear wherever it is used that this savings example is not showing the average savings of customers but is rather a hypothetical example," Muszynski said. (It assumes a borrower's interest rate is nearly halved). "All are pretty aggressive in their marketing," said Mark Kantrowitz, the publisher of SavingForCollege.com. The key takeaway, he said, was that "you should be skeptical about the average savings figures." Before you refinance your student debt, use a loan calculator (Kantrowitz has one on his website) to compare the monthly payments and total bill of your current loan against a potentially new one. "Keep in mind," Kantrowitz added, "a longer repayment term leads to lower monthly payments, but also more interest paid over the life of the loan."

Loss of consumer protections