Metrum Acoustics has my headphone amp. How do I get them to give it back?

Hi. I've been trying to get an Aurix headphone amp repaired by Metrum Acoustics for 10 months. They've stopped responding to any of my emails, and they still have my amp. I just want it back at this point. I'm not sure if they've gone out of business or are just that terrible at dealing with customers.

Here's the story in chronological order:

Apr 30, 2019 - Contacted Metrum Acoustics about a repair of my Aurix Headphone Amplifier. The left channel had some crackling and distortion.

May 1, 2019 - Heard back from Maria at Metrum Acoustics. She offered me to upgrade and purchase an Amethyst. Price was a bit high and liked the amp I had, I declined, and said I'd just like to get mine repaired.

Jul 18, 2019 - After spending most of the summer engaging in back and forth with Maria and the repair department trying to convince them that the amp needs a repair, they finally agree and send me an RMA form and an address. I'm out of the country by this time for work. I tell them I will send the amp as soon as I return.

Oct 1, 2019 - I ship the amplifier to the Netherlands for repair. I receive confirmation from UPS that it has been received by Metrum Acoustics.

Dec 1, 2019 - I've heard nothing about the status of the repair, so I write Maria. The email bounces back; her address is no longer active. I write the support email address.

Dec 3, 2019 - I get an email back from Wouter Hazenberg. He says "I expect the repair to be done beginning of next year. There’s quite a backlog. And repairs of our devices take much attention to detail." I thank him for the update.

Jan 27, 2020 - I write with a very cordial email inquiring about the status of the repair, stressing that I understand that quality takes time, but that since it was the new year I was curious when I should expect the amp. I receive no reply.

Feb 10, 2010 - I write a follow up email. No reply.

Feb 25, 2020 - I write another email inquiring. No reply.

Feb 29, 2020 - I write an email saying: "I’m very upset. I don’t know what else to do.You have in your possession an amplifier which cost me $1000. I want it back.You ignore all my emails. If you can’t fix the amp, just apologize and send it back to me."

I receive no reply.

I can only assume that this company has either gone out of business or has no intention of returning my property.  Has anyone encountered this situation either with Metrum or another manufacturer? If so, what did you do? Should I report a theft to the Dutch police? It seems crazy to me, but here I am.