Is this a prepaid or postpaid account? Either way, if your line has been disconnected "for months," you most likely do not have an account. I suggest contacting customer care or T-Force to sort out what happened to your payment, as it is difficult to apply a payment to an account that does not exist. Furthermore, you will probably have to establish a new line of service with a new account.
To contact T-Force
Go to the Contact Us page and use the Facebook, Twitter or Google Plus link under in the “Social Support” section.
Manage your T-Mobile account