UPS failed to deliver thousands of packages by their estimated arrival dates, leaving people across the country without their gifts on Christmas. UPS, the largest package delivery service in the world, said it simply had too many packages to deliver ahead of the holiday.

“The volume of air packages in our system exceeded the capacity of our network, as demand was much greater than the forecast,” UPS spokesperson Natalie Godwin said in a statement Tuesday. “As a result, a small percentage of shipments are delayed and will not be delivered today.” That was the last day customers could receive Christmas gifts on time, as the company did not make deliveries on Christmas day. UPS did not disclose how many packages were running late.

She added, “We are using every available resource to get packages delivered.”

Who’s Affected By The Delays?

Customers nationwide were affected by UPS’s delayed delivery. Those in the Dallas-Fort Worth area had additional delays because of severe weather last week, but UPS said people in that area still should have received their shipments by Dec. 24.

And Amazon Prime members, who receive free two-day shipping through a partnership between Amazon and UPS, were particularly upset by the delays. According to the company’s policy, these customers can request refunds through the website and may be eligible for a free month of the Amazon Prime service.

We have a relationship with Amazon. We will definitely work with all of our retailers,” said spokesperson Natalie Black. “We’re going to make good on our service commitments. What that exactly entails I don’t know, but we’ll work with them to maintain that relationship.”

Backlash Online

Some angry customers have taken to social media to voice their opinions, using hashtags like #UPSsucks and #UPSfail. To its credit, UPS responded and apologized individually to many of the riled customers.

4 days after it was expected, still no delivery from @UPS #wheresMyPackage #wheresUPS #fail

— Ian Goldstein (@IanSGoldstein) December 25, 2013

UPS says it delivered my package to the "front desk" of my apartment. My building doesn't have a front desk you ass holes! #wheresmypackage?

— Will (@Will_Neff3) December 25, 2013

There are no words for how furious I am at @UPS right now. #wheresmypackage

— seth. (@plunkseth) December 24, 2013

Black said that the remaining packages should be delivered by Friday, adding that people who were guaranteed delivery by Christmas would receive refunds.

In most cases, however, UPS does not guarantee delivery in time for Christmas for ground shipping sent after Dec. 11.

FedEx Reports Problems

UPS isn’t the only service reporting holiday delivery problems. FedEx also experienced a backlog of packages, though to a lesser extent.

We’re sorry that there could be delays and we’re contacting affected customers who have shipments available for pickup,” FedEx spokesperson Scott Fiedler told the Associated Press Wednesday.

Fiedler also gave an idea of the load FedEx had. He said the company has handled 275 million shipments since Thanksgiving, adding that “very few” were not delivered in time. As with UPS, FedEx refused to state how many packages were held up.

Both UPS and FedEx were probably strained not only because of weather delays but also because of a shorter holiday season. This year, there were only 26 days between Thanksgiving and Christmas, potentially leading to more last-minute shopping than usual.