Two consumer groups said on Thursday that some of the largest U.S. auto insurers, including billionaire Warren Buffett’s Geico Corp, are short-changing customers on premium rebates as Americans drive less due to stay-at-home orders aimed at curbing the coronavirus outbreak.

U.S. auto insurers will return a total of more than $7 billion in premium refunds and credits to customers through May, according to the Consumer Federation of America (CFA) and Center for Economic Justice (CEJ). Still, the drop in auto insurance claims spurred by reduced driving is far greater, the groups said.

The groups created a report card for premium relief from the nation’s 15 largest insurers, giving Geico Corp., part of Buffett’s Berkshire Hathaway Inc, a “D-” and National General Insurance and “F.”

Insurers’ relief to consumers ranges from 10% to 35% of two months of premiums, with the “vast majority” of insurers giving back 15%. Some data shows motor vehicle accidents were down 50% or more, the CFA said.

The largest U.S. insurers began issuing premium relief following pressure from consumer groups. Allstate, on April 6, said it would return more than $600 million to customers, or 15% of their monthly premium in April and May.

Geico, on April 7, said it would offer about $2.5 billion of credits to 19 million auto and motorcycle policyholders between April 8 and Oct 7.

“We were concerned that a credit for two or three months might just expose our customers to large catch-up payments once events returned to normal,” a Geico spokesman said in a statement about its “D-” grade from the groups. “We acted swiftly to implement a credit across the entire policy term so our customers would see relief for an entire six months.”

A National General representative did not immediately respond to a request for comment. The groups said the insurer is among several that have still not acted to provide relief.

State Farm, which said it would return $2 billion to customers, a 25% premium credit on average, and American Family Mutual Insurance Co, which said it is returning $200 million, both received a grade of “A” from the groups.

The Travelers Companies Inc, which said it was giving U.S. personal auto insurance customers a 15% credit on their April and May premiums, received a “C+.” A spokesman did not immediately respond to a request for comment.