I believe if you are still the registered owner of the domain (listed in the whois for contact info and registrant, your name, your email, your address), you can do what you want with it. If the ownership was transferred to them, things change and probably SOL.
Yeah, that's the thing I'm not sure about. If giving them admin privileges is "ownership transference" since I can't login to see who is listed as owner. Maybe my name is still on it and they simply changed the contact info, billing, admin info.