Do I have any legal claim for my complete severance?

Question:
I started working for company X in August 2016 (12 month contract).

In Feb 2017 I was told that company X have set up a new independent company, company Y, to deal specifically with the after-school programs.

So in March 2017 I was given a new 12 month contract with new terms with company Y.

I was told, in writing in an e-mail, that nothing would change and that i was EXTENDING my contract another 12 months with company Y.

2 months or so ago I got a letter of release (just to be safe) stating that I had worked for Z (Z is the name of the main company/program that X and Y ran) since August 2016 and would finish my contract on Feb 2018.

Now company Y is saying they do not owe me 19 months severance but only 12, because they are company Y not X, and that what the previous manager had told me was "wrong".

Do I have any legal claim for my complete severance?

Answer:

You may have a claim on the grounds you described but I would not trust a labor inspector to get this one right. Without that letter and a lawyer, and since the companies were different companies and registered under different business licenses, on the surface you are not entitled to severance from the others because you did not complete a full one year of work for them, which is the minimum time required to qualify for severance. The letter would change that provided it is signed, stamped and not sent to you via email, but I'm certain you'd need a lawyer to use it.

Note: The problem is more of a cost-benefit analysis. It's 7/12th's of 1 years severance, so likely ~1.2-1.4 million won. A lawyer would definitely charge more than that, and going to court would cost at least 1 million. You can try the labor board but I just do not think a labor inspector would rule in your favor.