Most likely, your bank account or your computer was compromised.
Do you have a reputable Antivirus program? i.e. Malwarebytes
Full Scan with the Antivirus
Scan your computer with your Antivirus software.
Does your Computer infect with Rootkit?
Malwarebytes’ AdwCleaner is one of the best cleaners for eliminating rootkits.
Download here: https://www.malwarebytes.com/adwcleaner
Update ALL of Your Web Browsers
You should always ensure your web browser is running the latest version. An update can come with new security features, compatibility fixes, and plenty of other goodies that can enhance your browsing experience. It might also fix any browsing problems you might be having, including login issues.
Disable Your Browser’s Extensions
If you use browser extensions, like an ad blocker or a password manager, they might interfere with the bank’s login systems. They could accidentally hide a form field or intercept the connection and cause an error. Some third-party extensions have keylogging feature, inject malicious codes or monitor your web activities.
Make sure the Firewall is Enabled
If the firewall is disabled or some features were turned off, restore to the default settings.
Check the Event Viewer
Disable Suspicious on Startup
Look into the Task Manager, and click the Startup tab to examine any unnecessary programs.