You obviously have a legal right to control over the IRA. However, in deciding how to get to a position whereby you can reassert that control, it will help to consider things from their point of view:
They have a "several years" old, dormant account. It will have certain details associated with it, including the name of the (now defunct) company that ran the original 401k and (what they believe are) the details of the beneficial owner (name, address, date-of-birth, etc.).
"Someone" contacts them claiming to be the original beneficiary. That person has (or claims to have) the same name, (presumably) can quote the original company name, might or might not live at the same address, but whose (presumably provable) date-of-birth does not match what they have in their records.
At a time when the threat of identity theft is (at least perceived to be) high, it is understandable if they do not immediately turn control of the account over to you. There appear to be a dozen K J Gregory's on Facebook, so (from their point-of-view) it's quite plausible that the person contacting them is not the same person as the whoever originally owned the account.
In short: they are (almost certainly) not denying you access out of spite or malpractice (that would warrant a legal solution)... they are simply being cautious (perhaps over-cautious) about identity theft.
The Solution (or, at least, the next steps)
You need to remove their doubts that you might not be who you claim to be, and are – in fact – the original owner of the account.
Calling on the 'phone or submitting online is not the way to handle this. As noted elsewhere, customer service people have limited flexibility and online processes have almost no flexibility.
Instead, I would suggest you gather together any applicable evidence you have easily to hand, for example:
- Documents from your time at the original company, especially:
- Anything to tie you to the original 401k.
- Anything to tie the owner of that 401k to your real date-of-birth.
Proof of your real data-of-birth.
If you have moved since that time, anything to tie you to the address they have on file.
Essentially, you want to show something like IRA number
XXXXXXXX (against which they have the wrong DOB), came from 401k number
YYYYYYYY and that the owner of that policy had your real DOB.
Send what you have with a firm, but polite covering letter setting out the situation, including your belief that an incorrect date-of-birth got entered somewhere along the line. Include copies1 of whatever supporting evidence you have. State that you believe this demonstrates your right to control of the account, but that they should let you know if there is anything else they require.
Ideally, see if there is a department dealing with unclaimed/dormant accounts that you can send it to. Otherwise, a "dispute resolution" department of something like the "Customer Service Manager".
Only if they are completely unresponsive to this type of approach would I consider "lawyering-up".
1 It's possible they will want to see originals at some point, but I would send copies initially.