License violation e-mail from COPYTRACK GmbH regarding purchased image from Adobe Stock

Hello,

I received today an e-mail from company Copytrack GmbH as following: 

Regarding your publication on : www.prii....
Dear Sir or Madam
COPYTRACK GmbH manages the image rights and image licences of photographers, picture and news agencies and other companies with image rights.
One of our members has determined that your company is using images and making these available to the public but cannot recall having a license agreement with you. Of course your use of those images might be legal. This is why we ask you to provide sufficient proof of license, since otherwise an unauthorized use of the images is a copyright infringement.
If you are not able to provide that proof, in the interest of fairness our member is offering you an opportunity to purchase a license for your image use ex gratia retroactively. You would retain the right to continue using use the image.
Without a retroactive licensing a legal enforcement of the license and damages will be inevitable. Removing the image from your website will not inhibit these steps.
More information about the image you are using can be found under your case number, XXXXXX, on https://portal.copytrack.com/en/start
We ask that you reply by Monday, 30. Dec 2019 at the latest. etc, etc, etc ...