After a year of relief, robocalls are back up to pre-pandemic levels.

Americans received more than 4.6 billion robocalls in February, up 15% compared to January, according to new data from YouMail, a robocall-prevention service that tracks robocall traffic across the United States. About 159.1 million robocalls were placed each day last month.

This marked the highest monthly robocall volume since February 2020, notably right before the Covid-19 pandemic hit the United States hard. So far, 2021 is on pace to reach 51.5 billion robocalls, a big jump from 2020 (45.9 billion). Americans received 58.5 billion robocalls in 2019, up 22% from the year before.

"Because February was a short month, I think the first two months are lower than we'll see going forward and we're actually going to wind up much closer to 2019's pre-pandemic levels overall," YouMail CEO Alex Quilici told CNN Business, attributing the resurgence to economies' reopening worldwide.

Americans experienced a significant drop in the amount of robocalls flooding their phones last Spring, helped by international call centers being shut down during the global pandemic and government efforts to stop Covid-19-related scams. At the time, YouMail reported the number of robocalls made to US phone numbers in April was the lowest in two years. That included both scam and legitimate calls, such as payment reminders from banks.

"Call centers are closed or running at much lower capacity due to social distancing around the world," Quilici told CNN Business at the time. "There's no point to robocall people if there's no one there on the other end [to field it] when someone 'presses 1' or returns a call."

The latest report noted that scam and telemarketing calls accounted for about 60% of last month's robocall volume -- a trend in line with past months. The leading illegal types of robocalls involved car warranties and health-related scams.