How to find out someone really holds a Doctorate in Electrical Engineering from Hungary?
You could try writing to someone who teaches mathematics there --- see the course coordinators listed here. Pick someone who is likely to have heard of you (or your Ph.D. advisor, or any of your co-authors, or someone who might be marginally interested in anything you've worked on) and make sure the email subject line reflects this connection. I've done this sort of thing MANY times, even a few times in the early 1990s by postal mail. Also, try writing to a reference librarian, something I've also done successfully several times.

To hopefully not overstate the obvious, if you write to someone in mathematics (a field I chose because you said you are in mathematics), this person is almost certainly not going to know the answer to your question, but he/she should be able to assist you in locating someone who can investigate your question, and you should be clear about this in your email to any such person in mathematics.