Indians suffer the most when it comes to spam calls from network providers and telemarketers.

On an average, smartphone users in India receive some 22 spam calls a month, the most in the world, according to a July report by Stockholm-based phone-number identification app Truecaller. The US and Brazil came in second and third, respectively.

Truecaller studied over 5.5 billion spam calls around the world between Jan. 01 and May 31. The data was collected anonymously from incoming calls that were marked as spam by users or automatically flagged by the Truecaller app.

In India, the rapid growth of telecom services over the last decade—the country has over 1.12 billion registered mobile users—has made spam calls an increasing concern. And behind these calls are the usual suspects: mobile operators, debt collectors, banks, and telemarketers, among others.

“India’s spam call issue lies with operators and financial services. Many of these operators are seeking to provide special offers for free data or unlimited calls. Which doesn’t sound so bad—until you get bombarded by them,” Truecaller said.

Over 50% of the spam calls received by Indian smartphone users come from network providers offering data plans or new promotions, according to the report. The second-largest culprit is what Truecaller labels as “nuisance calls,” typically entailing harassment or pranks. And this is a worrisome trend. In the northern state of Uttar Pradesh, for instance, women’s phone numbers are sold for a paltry sum to men who sexually harass them through phone calls.

To battle the growing problem of spam calls, India’s telecom regulatory authority (TRAI) has been devising ways to let users block unwanted contact. But as more and more Indians buy mobile devices—by 2018, over 60% of Indians are likely to have a smartphone—spammers are likely to find even more people to target.