Hello Sondra,
As far as I can tell, the initial $215 payment was not applied to my EIP, but to the monthly usage bill. Take a look at this image:
http://i.imgur.com/ex2ra7N.png (I would attach it here but the option to attach images is greyed out). The $215 payment made on July 1st was made with the ETF refund card I got, believing it would go into my EIP balance, but as far as I can tell it went into my monthly bill. The fact that I am being credited $48.36 off this month's bill seems to support this.
Likewise, you can see there as well as on the following image that a charge of $215 is appearing on my sister's plan in addition to the monthly $25.75 payment, for a total of $240.75:
http://i.imgur.com/Zu9F4cW.png
Here is the information on her portion of the bill. Even though it says it is "not a charge", the fact that I am being billed for it seems to contradict that:
http://i.imgur.com/vGgTIJP.png
I tried to find a history of my EIP payments but so far I haven't been able to see it. A payment of $166.00 made at a T-Mobile store should appear there. However, according to my calculations, it seems both the amounts of $215 and $166 have been subtracted from the EIP.
So as far as I can tell, T-Mobile applied the $215 payment to both my EIP plan and my monthly billing, and now is asking me to give the $215 they applied to the billing back. I really don't see where these payments "wash-out".
Any help in clarifying that will be greatly appreciated.