Agreed, this is the most important. And go ahead and bring key documents - driver license, passport, lease/rental agreements, last year's taxes, a previous statement you have from them, whatever.

Anything that will help you prove: a) you are who you say you are and b) this is your account will be useful.

And if you're physically in their office, they can and will follow the backchannels to get a better result faster than you can over the phone.