First of all, I ask of you to be kind and patient, since this is my firt post and I'm not feeling myself today.

*If you want to skip the problem at hand and go straight to the warranty issue, go to the fourth paragraph.

Starting from the beginning, I bought the "new" DJI Phantom 3 SE in China when I went to visit there. If you haven't heard about this drone, it's a mix of the P3 Professional and the P3 Standard that just was made available globally. After having it sent separately to Europe (I couldn't put the whole box in my lugagge), I arrived home, unboxed it and tried it out with one particular 16 GB Class 4 Sony microSD card. It seemed to work fine.

After purchasing a better and bigger microSD Card, I inserted into the drone and I was surprised to see that it had the "SD Card Error". That particular microSD card in question was a 32 GB Class 10 Samsung Evo. I bought several differente cards from that moment on, to see if it was a problem of the Samsung one or it was the drone. Turns out it was the drone. I got my hands on more than 5 different SD Cards from all different brands (Kingston, other Sony cards, SanDisk, Lexar, Transcend, etc) and different speeds and sizes. None of them worked.

At this point I was pretty desperate, since for some particular reason the only microSD card that worked "fine" was the original Sony 16 GB class 4. However, it is widely known that with this speed, the video capabilities are severely limited in itself, and 4K recording is impossible. It is also worth noting that everytime I would try a different card in the drone, the surface of the gimbal would become extremely hot, well beyond the safe limits.

The logical thing to do after this would be to request the repairing of a product that has cost you a lot of money, is defective and is still under warranty(the drone was bought in the beginning of June). I did so, and requested an RMA here in Europe, where I normally live. Next thing you know I receive an e-mail from DJI saying, literally, "No Warranty! P3 SE gimbal is not recognized & sd-card won't work, but the P3SE unit was bought in China CE so no warranty services can be provided!"

Now this is completely illogical, since I had the option of choosing my particular model of P3 SE when soliciting the warranty repair service, which implies that the warranty does apply to it. Not only that, but I was assured by the company in which I bought it that I would have coverage back in Europe. Now they're asking 119 euros for nothing, since they haven't touched a thing in the drone and my P3 SE is being held hostage against my will in the Netherlands

If possible, I would cherish some advice or tips on how to continue next.

Thanks for sharing your experience with us,  deeply sorry for your situation and I can totally understand how you feel about it.
While I'm very sorry to tell you that we do not provide international warranty recently, which you can find on our official website as well: http://www.dji.com/service/policy.
May I know more specific info about where you purchased it? It's appreciated if you could PM me the dealer's contact info so we can check why you're told that you would have coverage back in EU.
If you want to get it dealt with in EU, then you need pay for repair.