Cox lost may payment, won't do anything about it and is punishing me for it.

I use my bank to automatically send my payments to cox.  Last month was no different, except that cox seems to have either lost or stolen my payment.  I have put in a ticket and I had received an email about sending information from my bank to prove that the payment was made.  I did so.  But it seems like the Cox Communications Receivables Management office won't do anything.

I am getting concerned about my future with Cox.  I have made my payments every month for the past 5 years.  And now they are charging me a late fee for a payment they lost and refuse to look into nor will the support staff tell me anything that is going on.