What is the procedure for a company to get a debt judgment against a person?

I received a phone call from a person claiming alleged debt of 8 to 10 years ago. Firstly I did deal with this company but I am sure I do not have outstanding debt and do not recall this alleged outstanding debt. I told him that after 3 years the prescription law apply. He said that I have a debt judgment against me from 5 years back. I told him that it is the first I hear about this, I was never informed. My postal address and telephone nr. is the same for more than 10 years. He reached me by this same phone nr. which is on their files. So, if they have my phone nr, why did they not inform my before now?

Also, I do not keep any legal documents regarding debt and such for more than 5 years, how do I prove anything?

So, is such a one sided judgment valid?