I'm looking through your tickets and trying to understand what exactly is going on.
ART is a supported part of our Advanced Services management packages, though you were told incorrectly that it was unsupported at the time. The representative responding to the ticket at the time was unaware of the policy difference between standard support and Advanced Services support. Upon getting this misinformation, the AS support was the easy target for the issue with webmail and passwords you saw a few months ago ... Plesk acknowledged these problems were a result of a software bug, not any changes made on the server.
In one of the current open tickets, Plesk's response recommends
http://kb.parallels.com/en/6171 as a possible solution after investigating, but the ticket turned to a request for management review at this point without any acknowledgment of that update ... were you able to attempt this fix?
I see that in subsequent updates, we've offered to waive the OS reload charges to get the server back to a blank canvas, but it's not possible to meet the request to do so without causing any downtime to users on the server (as the OS is wiped and replaced, the content has to be backed up and restored), so the next step is not exactly clear. Supervisors in Tech Support and Advanced Services have been involved throughout these tickets to assist, and I'm sorry that Plesk Billing has not worked as expected. I'll keep an eye on the accounting ticket (6144724PLNT) to see that it is handled correctly.
The phrasing of that ticket might cause some problems ... if you're looking to continue the troubleshooting process, you may need to update that ticket. The billing department read "removal of this service if its been added," and see it as "cancel this service on this server" instead of "make sure I don't get charged for this until it works" ... If you intended the former, no clarification is necessary. If you intended the latter, please update the ticket to clarify.