How do I switch credit cards for automated billing of services?

We have a subscription to Quickbooks Back-up for our company's Quickbooks account. We have a "new" credit card that we would like to set up as the billing credit card. Over a year ago I logged into my online Quickbooks account and changed the billing information to the new credit card. My old credit card continued to get billed.

I have called Quickbooks customer service several times - using the one year paid customer service package where you're supposed to have instant 24/7 access to CS reps. They had a VERY difficult timing understanding what I thought was a simple request - please change the credit card you bill. It's been over a year since I tried to deal with this and my old credit card is still getting billed. Basically, I gave up in frustration. How can I get the credit card that is billed for our back-up subscription changed once and for all?