Bran
I unfortunately just had exactly the same experience today... For a car that I rented on their website the 31/05, so it was already payed even.
People at the desk told me "We are not allowed to say it publicly on our website, or even refuse payments from those cards on the website, but we do not accept credit cards from Bunq, Revolut of N26 anymore"
First time I heard about this was in one of their mail yesterday. Needless to say how upsetting that is personally, but I also have very strong doubts about the legal aspect of this practice?
Funny enough I rented a car at Sixt in Slovenia in March this year, without any issue, using the exact same card!
For reference, also posted a complaint on klachtencompass. I hope at the very least that they will refund the whole thing. :(