Looks like your account didn't transfer properly, your site still loads from the old server which is why that part is working, but not accessing to admin panel.
This means we need to grab the account fresh from old server, lucky they are still online. However this is something I can not do so I have notified staff that can and are now awaiting his reply. Will let you know as soon as I hear back.
Ps. this type of issue is best reported immediately, I see you did login to the account in January and I would think you noticed then as well.