This case is not as simple as it would seem. Agency law is very complicated, much more so than just copyright law.
If I understand it, you allowed EyeEm to be your agent with the ability to sub licence through other agents. They have done this through Getty so Getty had a valid licence to sell the images.
Unfortunately my limited understanding of agency law is that terminating the contract with EyeEm does not automatically terminate the contract with Getty. Getty need to be informed and therefore to go after Getty, you need to show they knew the contract had been terminated. I assume this would be difficult to prove. You could go after EyeEm if you can show they were still selling either themselves or through sub agents, after you terminated the contract. Beware of terms and conditions you may have agreed to allowing them to resell after termination.
I would be very wary of handing such a complex case to a lawyer. In the worst case, if you loose, you could be handed the legal bill for both sides.. perhaps 20,000 per side. Simply maths say that risk is not worth while give the likely level of damages.
If you decide to litigate , then perhaps it would be better to do it yourself in the small claims track of the Intellectual Property Enterprise Court. For that there is a snag as I see EyeEm is located in Berlin. Germany does not have a small claims track. The EUCJ confirmed in Pez Hejduk. v. EnergieAgentur.NRW GmbH UK photographers have the right to claim , in the UK, against any copyright infringers in any EU member state where the images are visible on the web from within the UK. Unfortunately I know of no claimant who has been successful this in the IPEC SCT. The only claim I am aware of has, I think, probably failed, due to insurmountable problems with the bureaucracy.
While I would like to offer hope and help in finding a legal path to get you damages, in this case I don't think I would resort to litigation. That doesn't mean you shouldn't kick up a fuss and most certainly, you should inform all agents involved that they have no rights to continue distributing your work. That way if Getty does it again, you would have a much stronger case.
If your sufficiently annoyed that you are willing to take a risk with legal costs, then you should talk to an expert IP lawyer. If your going for EyEm in Germany then you could discuss it with an IP specialist such as
www.recht-hat.deThe one thing you case illustrates is why many top photographers are now moving to selling direct. In your case, you only have an agent and sub agent, however I have come across chains building up where each agent has passed the images to other agents so that you have sub sub sub agents, all competing with each other to be the cheapest. When any makes a sale then theoretically 50% ( or sometimes rather less ) is passed up the chain and so if a royalty eventually reaches the photographer, it is only a fraction of the selling price. Fortunately in some cases the royalty doesn't seem to find its way back to the photographer at all. These chains also seem to persist for years after the photographer cancelled his contract with the first in the chain.