Urgent – possible charges from shopping cart with error message

When purchasing course, then processing credit card … error appears that payment did not go through. In authorize.net it shows unsettled transaction. BIG PROBLEM is that it shows in bank as pending. This means that users can be submitting card info many times since they receive error message. I have contacted authorize.net and they said it is issue with developers of site and payment plug-ins. I believe support token is still active for this site.