Was laid off-(37 years with same company). Company finally closed. However, 5 years ago, company laid off 150+ workers and they were given severance pay. 20+ were retained and over the years others who have left or let go received severance. No severance for the remaining 20+ though. A few weeks before final layoff, two were let go and received severance. (They were the ones who were actually responsible for the company's downfall).
No policy written about severance but it was implied in several meetings. Then owner said
No severance - our severance was him allowing us to work for the past 5 years. I'm 57 yr/old - only job I've ever had. Too young to retire, many health issues... the company
Is not bankrupt but I don't believe the owner wanted to have to pay those who were left
Because we'd been with him too long and our severance would be too high. Life is not
Fair... you give your soul to a company and poof-it's gone. Not even thank-you. Just
Go away.

Yep companies are not loyal to employees. Be sure and sign up for unemployment and start getting the resume out to other places.
But unless they made some promise, not what they implie but a firm promice, you have little to go on, if they promised it to you, most likely you can sue for it. ** of course if you sue, you may not get a job reference from them, plus a future boss may not like the idea ofyou sueing them.
So it is all a gamble what is the best thing to do. Good luck in the job search.