I'd like to make this an opportunity, but definitely want things done right first. Since this software isn't mine or my client's software, but a service company

I'd like to make this an opportunity, but definitely want things done right first. Since this software isn't mine or my client's software, but a service company's, I'm a bit leery to just call them up and tell them, "Hey I have all the CC#'s for every transaction ever run through your system". So that's why I'm here asking for advice :)