Would like to terminate service

I was a satisfied customer, which seems rare reading the posts here.   In May, my credit card expired and I posted a new card number to the web site.  Apparently it didn't take.  I contacted the service representive after a lengthy wait and explained the issue and was told it was all resolved.

During a recent business trip I lost contact with my server.  Upon my return home I found I had been disconnected for non-papment.

My payment history for this year is:

01-02-127.85

02-02-132.85

03-05-132.85

04-06-132.85

05-11-132.85 <---this was when card expired and I paid manually giving them the new card.

Autopay was on until today.  My account is now showing a past due amount of 417.55.

This is unacceptable in light of the no notice shut-off.  If this is the "business class" it is poor business to do a no warning shut off with the wrong billing especially after all my payments have been automatic.  Please tell me how to cancel the account, get a final bill so I can move on to a more reliable carrier.