Customers of the German online bank N26 say they feel "outraged" and "betrayed" by the firm's decision to leave the U.K.

Berlin-based N26 announced last week that it would no longer be able to operate in the country as it won't have the appropriate license to do so after Brexit. The start-up will be closing all U.K. accounts on Apr. 15.

The firm made its U.K. foray in October 2018, over two years after the U.K. referendum on its EU membership and six months before Brexit was initially planned.

Miguel Frias Mosquea, an N26 customer based in London, told CNBC he felt "outraged" N26 had blamed its U.K. departure on Brexit: "It's fake news."

"Surely they need an excuse for investors and blame it on Brexit, not on mismanagement or lack of knowledge on how to tackle the U.K. market," the 33-year-old said. "It's better to pretend it's not their own failure."

Another, Ian Cook, said he felt "disappointed" by N26's U.K. closure, saying he was a fan of the firm's offering, having started using it in July 2019.

"They are still my only bankers so I haven't used any other banks," Cook, who is based in the English county of West Midlands, said. "I prefer N26 over other banks because of the 'extras' that come with the accounts."

Cook, 62, said he also felt "betrayed" as N26 "never gave any indication that the U.K. leaving the EU would make trading difficult for them." He added: "I don't believe Brexit was to blame."