Even if it's years ago, as the quoted email said, their customer service may help if you can provide enough proof of ownership (minus the password).
But what kind of proof does OP have? Does list of bitcoin address and rough date when the wallet is created/last serve as valid proof?
The case is messed up.
Mattgillum had the identifier and the password.
There could be one possibility to verify that he indeed is the owner of the identifier.
- Give them the identifier and last/first few characters of the password.
It's still risky because he has to trust the guy in the customer service for this. The best shot for his is by any chance if he has the 12/24 word seed then he can restore the wallet using Electum. But he has to have the seed.