Thanks for joining our Support Community to find out more about what happened to the balance on your account. You're right, this sounds pretty confusing and it'd be nice to get to the bottom of what happen to the remaining amount. I hope I'm not too late to your reply but I recommend getting in touch with our T-Force team via Facebook or Twitter to have them research your account as you won't get any more info from My T-Mobile. Please keep us updated!
Amanda left a really good suggestion here. Have you had the chance to contact our T-Force team? If so, please keep us posted on if things got squared away. Thanks!