It's not your imagination. You are getting bombarded with robocalls.

Robocalling, a practice where marketers send automated voice messages to thousands of phones at once, surged 60 percent in the U.S. last year to 48 billion calls, according to preliminary year-end data from YouMail, a robocall management company that tracks the volume of calls.

"Scam calls have been increasing very steadily, and it's driving people to not answer their phone," said YouMail CEO Alex Quilici. "It's driving people to not answer their phone and it's kind of created this death spiral of phone calls as the robocallers ramp up their efforts, and the legitimate roboccalls try harder to get through."

Both mobile carriers and smart phone makers are racing to keep up with the influx, but have been unsuccessful so far because the technology to deploy the calls is cheap, easy and lucrative for scammers. Scams make up an estimated 40 percent of all robocalls, Quilici said, while the other 60 percent are "legitimate" robocalls, like those that come from pharmacies, libraries, schools and political candidates.

"New, inexpensive technology and products have enabled scammers, including those located outside the U.S., to set up mass calling operations that can place high volumes of spoofed calls with minimal investment," said Andrew Morgan, a spokesman for AT&T. "We will have to continue to find new tools as illegal scammers adjust their techniques to overcome the latest innovations."