Thousands of public servants have been trying to report overpayments issued by the problem-plagued Phoenix pay system before a looming tax form deadline — only to get a busy signal.

The Phoenix call centre, which typically gets about 2,000 calls a day, was hit with 12,000 calls Wednesday, causing the overloaded system to drop most calls.

The volume took Public Services and Procurement Canada, the federal paymaster, by surprise and left it scrambling for another plan.

The department sent a notice to all deputy ministers late Wednesday saying that employees also can use the Phoenix feedback form to report overpayments online, which should reduce the volume of calls swamping the call centre.

The notice assures employees that no “further action” is needed to report the overpayments once the pay centre is alerted through the Phoenix feedback form.

It’s not clear why the call volume exploded so suddenly. Departments were notified last week that their staff should inform the government of any possible overpayments in 2017 by Jan. 19 to ensure they are recorded in Phoenix by the end of the month.

As long as that’s done, employees will only have to repay the net amount of overpayments they received and not the gross pay, which includes taxes and other deductions. Employees should get a letter by early February confirming they only have to repay the actual amount they received.

Employees who aren’t recorded in Phoenix by that deadline will have to repay the gross amount.

Some public servants say they have tried unsuccessfully for days to get through to the call centre’s (1-855-686-4729) hotline to report their overpayments. A newly posted YouTube video showed a woman unable to get through after calling several times a day for a week.

“I can’t even get through to a voicemail, leave a message. Nothing. There is absolutely no chance I can record my overpayment if that continues. I am a week into phoning this number several times a day and I can’t even get connected. Don’t know where to go with that,” she said.

This is just the latest source of frustration for those who have been overpaid by Phoenix since it was launched.

The government maintained that tax laws compel employees to repay the gross amount of the overpayments rather than the net amount they actually received. That prompted an outcry. The complaints resonated with many MPs, who felt being forced to repay the gross amount was unfair.

The Public Service Alliance of Canada proposed a blanket exemption so no one would have to pay the gross amount. Instead, the government gave employees a reprieve and allowed those who reported overpayments by the end of January to pay the net amount and have their tax slips adjusted.

For those who don’t make the deadline, the government will delay collecting repayments from them until after Canada Revenue Agency has processed their tax returns and they have received tax refunds.

The department said these employees will receive amended 2017 tax slips that show their correct annual earnings, as well as any taxes on the overpayment, and they will be eligible for a refund of the tax withheld.

Also, those who received overpayments worth more than 10 per cent of their biweekly pay can put their repayments on hold and follow up with the government for a flexible repayment plan.

PSPC says it can’t confirm how much money has been issued in overpayments or how much of the backlog — which, at last count in November, stood at about 619,000 cases — is made up of overpayments.

The most common overpayment situations are employees moving to a new job and getting paid twice or continuing to get paid after they quit, retire or finish a contract.