You can pay many of your household bills at Oxxo.  Simply bring the bill in, they will scan the bar code.  They will often show you the account number – make sure this is correct.   There is a small commission charge, usually around 10 pesos.  KEEP YOUR RECEIPT in the event you have to prove that it was paid.  Usually you have to pay these bills in cash, if they say you can use your credit card, don’t be surprised if it is declined.  It’s not a credit card issue, its an Oxxo issue.