why "sync'g successfully" message if xmarks acct invalid? sync'g where?

My laptop has been set to sync with a particular Foxmarks (Xmarks) account for years. Everything syncs automatically, or so I've thought. I haven't visited the Foxmarks/Xmarks site to check things; I guess I figured that I'd get an error message like "cannot sync/login to account" if the application was not able to sync or connect. Today I visited the laptop settings via FF add-on. Current status says "syncing successfully" and has today's date (pretty sure I've checked here before and this date is always within the last hour or so).

The problem appears when I try to manage profiles. The my.xmarks.com button takes me to the site, which does not recognize my username (checked caps lock, etc.). Site says username is not registered.

If this account (I have more than one account and the other is completely fine - I've checked) has been deleted (during Foxmarks to Xmarks transition, maybe), with what/where/who has my data been syncing all this time? Is anything retrievable? What is to be done?