HARRISBURG — Calls to the state’s unemployment compensation service centers have mysteriously skyrocketed since September, and the agency doesn’t know why.

The volume of calls to the centers rose to nearly 8 million in September, compared with slightly more than 900,000 a year earlier, Labor and Industry Secretary Julia Hearthway told state lawmakers in a letter Monday. In October, calls exceeded 11 million, and then reached 15.5 million in November.

The problem is all the more perplexing because the unemployment claim caseload is on the decline, measured either by number of initial claims or by the duration of claims, Hearthway wrote in the letter, obtained Tuesday by The Associated Press.

“We are looking at all possibilities that may explain this dramatic increase,” Hearthway wrote.

State legislators have been fielding complaints from constituents, said Erik Arneson, spokesman for the Senate Republican caucus. He welcomed Hearthway’s letter, saying eligible claimants deserve to have their paperwork processed without an undue burden.

“When a person loses their job and reaches out to a service center for help, the very least they expect is for somebody to pick up the phone and talk to them,” said Bill Patton, House Democratic spokesman. “For hundreds of thousands of Pennsylvanians without jobs, that is not happening.”

Labor and Industry Department press secretary Sara Goulet said many of the questions that come in through the number can be answered online, and the state has dedicated a fax number to help direct people around the problem. It generates a call back from a staff member within three days, Goulet said.

Other alternatives include going to one of 68 Pennsylvania CareerLink centers around the state, where open phone lines are maintained.