Your balance isn't gone, don't worry!
We find that sometimes when our members update their app or log out after having been logged in for a long time, they can accidentally create a second account that has no claims in it and therefore no balance. Creating a second account on the same device is against our Terms of Service, but don't worry - we know these things happen. (Feel free to read our Terms for more details.)
In order to get your balance back you simply need to log back into your original account.
You will need to determine what email address your old account was related to. To do this, look over any of the past emails we've sent to you and double check the email address that you provided us with.
Remember that if you have forgotten your password, you can always recover it by clicking the "I forgot my password" link on the login screen of the Checkout 51 app.