EIP extra payments no applied to Balance

As of last month I have been attempting to pay an extra $60 towards my EIP via T-mobile website....no sooner when it accepts my $60 payments. it shows a reduction in the balance and 1 less remaining payment...Although weeks later my Auto Draft for my Monthly Family Shared Account deducts the $60 from my Family Shared Account Balance...and Increases my EIP back to the original balance.  for example...My balance last month for my FSA billing was $153.45 due for auto pay on 9/5/2013.  I made 2-$60 payments towards my EIP balance ...Yet currently  my FSA account shows a credit of -$120 and the auto pay only deducted $33.45 for my bill.......I spoke several times to a customer service rep and I receive conflicting stories....I noticed someone else stated they Had similar issues and  the"T-Force" department fixed their issue...........T-Force...please resolve my issues....I plan on paying an additional $60 mthly until its paid off...Please advise.