It's possible that the amount on the actual bill may defer. This happens whenever there is either a credit of some sort or payment applied after the invoice was generated. The amount on the bill doesn't change, it's generated on your billing cycle date and remains as is to give you a total of what your monthly charges, payments and credits came out to for that given month.
In this case I would suggest logging into My Account and verifying the section that reads "Current Balance". This is the most up to date balance in real-time and takes into consideration any payment we received after your bill was generated.
I hope this helps clarify things a little! 🙂