Seems that the general "FT consensus" in this type of situation is that whomever "promised you an upgrade" on a reschedule/irrops re-booking/etc should be gifting you some type of cert which would be used to confirm/uphold the upgrade. Otherwise, as in your case, the upgrades tend to vanish into thin air.

Have you checked your account to see if any certs were added unexpectedly?

Not sure what recourse you have in this case as its your word against theirs.

Craig