You have probably reached the daily, weekly or monthly spending limit imposed by your phone company. This limit varies depending on country and phone company and the only remedy is to wait.
You may also have reached the 500 USD credit limit per 60 days imposed by RPGStash.com in which case the solution is to provide us with photocopy of your phone bill and id. We will then be able to lift the limit for you.
In case your phone is prepaid, make sure your balance is sufficient to complete the payment.