Unfortunately nobody here can help.
PM worked by using the same serial number from one version to the next and those old numbers won't be accepted by the upsell installer.
You're going to have to call back and insist on speaking to a supervisor. If that doesn't work, get case numbers and names.
My PM 6.5 is 17 digits (and the dash). Does the PM serial number show up in your Adobe account on-line? If not, register it first. Do you still have it installed? Take a screen shot of the about screen. Register on-line. It will ask for the previous PM number.
Take care, Mike
That’s not the problem. Anyone who upgrade TO PM6 or later had a serial that InDesign won’t recognize.
This has to be handled through Adobe.