Delta Air Lines Chief Executive Ed Bastian says the airline has issued $6 billion in refunds since 2020 for canceled or significantly changed flights and detailed steps it has taken to improve customer service.

“Since the beginning of 2020 we’ve refunded over 11 million tickets totaling $6 billion, of which 20% has taken place in 2022,” Bastian wrote Transportation Secretary Pete Buttigieg in a letter made public Wednesday.

He also disclosed Delta automatically deposited an extra 10,000 miles in the frequent flyer accounts of travelers who experienced travel interruptions between May 1 and July 7.