Americans are now getting so many robocalls on a regular basis that many are simply choosing not to answer the phone altogether.

That’s one big takeaway from a report released Tuesday by Hiya, a Seattle-based spam monitoring service that analyzed activity from 450,000 users of its app to determine the scope of unwanted robocalling – and how phone users react when they receive an automated call.

Consistent with other analyses, Hiya’s report found that the number of robocalls is on the rise. About 26.3 billion robocalls were placed to U.S. phone numbers last year, Hiya said, up from 18 billion in 2017. One report last year projected that as many as half of cellphone calls in 2019 could be spam.

While many businesses have legitimate purposes for using robocalls – think package delivery services, home maintenance technicians and banks – unwanted robocalls represent a growing challenge for regulators and telecom companies.

In its analysis of a month’s worth of calling data, Hiya found that each of its app users reported an average of 10 unwanted robocalls. Many more incoming calls, about 60 on average, were from unrecognized numbers or numbers not linked to a person in the recipient’s address book.

What’s more, about half of cellphone calls are being answered at all, according to Hiya, whose systems integrate with lists of known and suspected spam numbers maintained by the Federal Communications Commission and the Federal Trade Commission.

“As our phones continue to be inundated by robocalls, many people no longer want to pick up the phone at all,” said Hiya CEO Alex Algard.

Federal regulators have moved to crack down on unwanted and spam communications, levying massive fines against those who have illicitly harassed people on the national do-not-call telemarketing list and adopting rules facilitating the rollout of new technologies to stop unwanted calls.

Earlier this month, T-Mobile said it would soon activate a technical protocol known as SHAKEN/STIR, a type of caller authentication program that follows the same principles as website encryption. Other carriers, including AT&T, Verizon and Sprint, have also committed to implementing the feature.