What happens? Any error message? How are you trying this? On the app, on the website, by text etc.? Maybe try a different way. If necessary contact 48 support. See the link in my signature below.
But you're logged in here on the forum so you should be able to log into your online account! If you can't then you'll need to contact 48 support. You can email them on support@48months.zendesk.com.