The problems come 18 months after a severe outage that forced RBS to set aside £125m to compensate customers and CEO Stephen Hester to waive his annual bonus.
Yesterday customers were unable to make online and card payments between 6.30pm and 9.30pm on what was expected to be one of the busiest online shopping days in UK history.
Affected people vented their anger on Twitter, with @CrispThirty tweeting: "The good news is NatWest's systems won't melt down again because they'll have a lot less customers after today #jokebank #natwest."
Meanwhile, BBC business reporter Ben Thompson used his account to highlight new rules enabling customers to switch banks more easily.
RBS – which owns NatWest – sought to reassure the public through Twitter, stating: "The systems issues that affected our customers last night have now been resolved and all of our services are now back working normally."
It has promised further investment in the technical systems, and offered to compensate those left "out of pocket" by the problems.
RBS customer services director Susan Allen added: "We clearly deeply apologise for the inconvenience we've caused."