> I'm thinking that may have killed it since you can't switch off the phantom before disconnecting the mic.
You can't have damaged the capsule that way. A capsule is just an air capacitor set in a specialized, acoustic "mini-environment".
Powering down before you disconnect a mike isn't to protect the mike; it's to protect all the other equipment from the spikes and thumps that can be generated--especially the power amps and loudspeakers in a P.A. system. If you have headphones on, it will help protect your ears as well.
So stop blaming yourself, OK?
--best regards
P.S.: BeyerDynamic US service was first-rate the last time I had any dealings with them, but it's been a decade or more. Please let us know how things go from here on.