US mobile subscribers received nearly 4 billion unsolicited automated calls in July, as efforts by government and industry to tackle the problem fell short, data from software company YouMail showed.

The company, which offers automated call blocking services, revealed the total number of such calls hit 3.99 billion last month, an increase of 54 per cent on July 2017.

AT&T customers were worst hit, receiving an average of 17.6 calls in July (see chart, below, click to enlarge), followed by T-Mobile US (16.9), Verizon (15.6) and Sprint (14.4).

The rise comes despite efforts by operators and the US Federal Communications Commission (FCC) to combat spam calls.

In 2015 the FCC passed rules meant to give operators and consumers more power to block unwanted calls, which were recently struck down by a federal appeals court.

Those were followed by the FCC’s formation of the Robocall Strike Force in 2016, a coalition of operator and industry partners headed by AT&T CEO Randall Stephenson tasked with developing recommendations to detect, prevent and filter such calls. Additional rules were passed in 2017 allowing operators to block calls originating from fraudulent numbers, known as spoofed calls.

At Mobile World Congress Americas 2017, FCC chairman Ajit Pai stated the issue remained his “number one consumer protection priority.”

But as Motherboard pointed out in May, the FCC’s focus on preventing calls from spammers and scammers leaves the door wide open for automated calls from debt collectors to continue.

In July, YouMail said just four of the top 20 automated callers in the nation were spammers or scammers. Indeed, the top five during the month were payment or debt collectors, with the lead originating number responsible for nearly 41 million calls alone.