FNB came in for criticism from irate customers on Monday after some couldn't access their funds, while some accounts displayed a R0 balance.
The biggest frustration for customers was, they claim, that FNB did not communicate that they were experiencing technical issues.
Downdetector, a local website which "detects when technology fails", showed a spike in reports from FNB customers from as early as 08:00 on Monday morning. FNB posted for the first time on both Facebook and Twitter that it was "aware of intermittent connectivity issues" after 13:00.
"We apologise to impacted customers for any inconvenience caused. Our technical teams are resolving this," it posted on Facebook at 13:22.
The same post was tweeted at 13:21.
FNB customers were not convinced. Echoing scores of other FNB customers, Peter Smith tweeted that "the connectivity issues" were "definitely not intermittent". "Have been waiting all day for these to be rectified. Please give your clients an update."
Tony Higgins felt FNB was "insulting" its customers by calling the "catastrophic failure" in its system "a connectivity issue". "I suggest you cut your bullshit and explain to users why they cannot access or transact in their accounts," he tweeted.
Another FNB customer Keith posted on Downdetector that all his accounts were mixed up. "Online banking crazy... my cheque account is now my e-bucks account and other accounts are named differently. Can't add a beneficiary to pay either," he posted.
FNB client Austil Mathebula told Fin24: "I couldn't access my account at all. I was so frustrated when bank tellers at Cape Town's FNB branch in Adderley Street said that their system had been down the whole day. They also indicated that it was a nation-wide problem."
"I immediately went on Twitter to see if there had been any communication about this from FNB, only to find that there was only one tweet in which the bank said there were 'intermittent connectivity issues' and they were working on resolving this. That was the only tweet I saw from them, and there were no updates as to what time the problem would be resolved.
"I had to make urgent payments. I feel they could have done better in keeping their clients in the loop about their progress in resolving the problem," he said.
Without elaborating on the cause of the problem, FNB said in a short emailed response to Fin24 that it "can confirm that intermittent connectivity and limited functionality issues have been resolved".
"We apologise for any inconvenience caused," the statement read.
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