CHICAGO (CBS) — Get ready for a summer of ripoffs. In the last four years, Illinois residents have overpaid more than $600 million for electricity, and it’s about to get worse.

Every time Elizabeth Davis, 96, used to turn on her lights, she felt like she was getting ripped off.

Her daughter explained alternative energy suppliers were charging Davis a lot more than ComEd.

Spark’s energy rate for Davis’ basement apartment was 9.94 cents per kilowatt-hour, compared to 7.219 cents charged by ComEd. Liberty charged her 10.8 cents for the first-floor compared to ComEd’s lower rate.

“I don’t even remember joining these people,” she said. “What they would do, they would call me late at night, and then they would call me in the morning.”

“It’s shameful to think that somebody like Ms. Davis, who’s a good Chicagoan, is getting ripped off because some alternative suppliers lured her into a bad deal,” said Jim Chilsen, spokesman for the Citizens Utility Board, a nonprofit nonpartisan utility watchdog.

Chilsen said alternative suppliers might become more aggressive this summer, because a new law that cracks down on dishonest sales tactics goes into effect in seven months.

“They’re going to probably be desperate to capture more customers before those new consumer protections take effect,” he said.

CUB pointed to statistics showing complaints about deceptive practices from electricity suppliers that have soared in recent years. In 2017, there were 1,401 complaints. One year later, it jumped to 2,388.

The agency also fears the summer will be ripe for bad deals, because ComEd’s rate just dropped to 6.72 cents per kilowatt-hour.

“Alternative suppliers are going to have a hard time beating ComEd’s rate this summer. So there’s a greater chance, a greater risk of being ripped off,” Cihlsen said.

So buyer beware is this summer’s motto from CUB.

One of the reasons consumers switch to alternative suppliers is because there have been times they offer better deals. The bottom line is, before you switch, make sure you compare the rates.

As for Davis’ allegations she was misled about electric rates, a spokesman for Spark said “Spark Energy does not condone misleading sales practices under any circumstance,” and Liberty said Davis “never filed a complaint, nor made any allegation of wrongdoing against Liberty Power.”