NEW YORK (AP) — Verizon said it resolved an outage that disrupted many U.S. customers’ calling and other cellular services for more than 10 hours on Wednesday.

The New York-based carrier didn’t specify what caused Wednesday’s disruptions, but confirmed that the outage was resolved by 10:20 p.m. ET. Verizon previously said it had deployed its engineering teams to address “an issue impacting wireless voice and data services.”

“Today, we let many of our customers down and for that, we are truly sorry,” Verizon wrote in updates shared on social media. A spokesperson later added that the company would give those impacted a $20 account credit through Verizon’s app, which on average “covers multiple days of service,” and directly contact its business customers with compensation.

Outage tracker Downdetector showed that Verizon customers began to report issues with their service around noon E.T. Wednesday. Reports appeared to peak in the early afternoon, but remained elevated later in the day. Downdetector said it had received a total of over 1.5 million reports before 5 p.m. ET.

Impacted users said their phones were in “SOS” mode or had other no signal messages. In cities like New York, alerts warned that the outage may disrupt 911 calls — urging residents to try landlines and devices from other carriers, if available, or visit a local police or fire station in-person in case of an emergency.

Other major hubs impacted by Verizon’s outage included Houston, Philadelphia, Dallas and Miami, per Downdetector. But many consumers across the country said they experienced disruptions.

A handful of outage reports for other carriers also bubbled up on Wednesday — but companies like T-Mobile and AT&T quickly confirmed online that their services were operating normally. Both suggested that their customers may have encountered issues contacting people with Verizon’s service, however.

When cellular outages happen, some phone companies also urge consumers to try to connect to Wi-Fi and use internet calling. If Wi-Fi is still unavailable, there can be a limited number of other options — including sending messages via satellite on newer iPhones.