Barclays customers have been reporting difficulties accessing money in their own bank accounts, and also in making payments, on Saturday and Sunday.
Some reported having their debit cards blocked.
The bank said on Twitter on Saturday morning that it was "experiencing technical issues" and that these were being "investigated urgently".
But on Sunday some customers said they were still experiencing problems in accessing cash.
"I have been repeatedly told the issue would be fixed by 5pm yesterday (Saturday) and still this morning it's in the same situation," said one customer who contacted the BBC.
Barclays did not formally reply to BBC inquiries, but said on its Twitter account on Sunday morning that it was "currently still seeing high volumes of customers calling us this morning, please bear with us".
It added: "If you need to check your accounts, please use our banking apps and online banking services, these are both running smoothly." Click Me