... the first time I emailed a PDF invoice to this company, there was no problem. They emailed me back acceptance, with a barcode string of numbers which [do not match] the one in the current refusal emails (above).
It's quite possible the company changed (part of) its procedure somewhere along the line. Alternatively, the duplicate number is due to an error. Either way, it seems futile to keep trying this door. You mentioned their "Contact Us" option is next-to-useless. I take it that's another email address. If its a phone number, how about that? Is there anybody you've dealt with before you could contact?
