Private student loan disappeared from my credit. Now a debt collector sent me a letter.

I had a private student loan with Navient. I graduated school in 2007, was unable to afford the payments. The loan went into default. Eventually I set up a payment plan to have funds automatically taken out of my bank. It went like that for years, until COVID. After the student loan freeze they were still taking the money out every month, then suddenly stopped. I figured they were part of the loan freeze.

They never resumed taking money out of my account. Then disappeared off my credit report about a year or 2 ago. Just got a letter and a text message from General Revenue Corporation looking to collect. Do they have any legal standing to take legal action to collect.